Multistandard video decoder and decompression system for processing encoded bit streams including a video formatter and methods relating thereto

ABSTRACT

A pipeline video decoder and decompression system handles a plurality of separately encoded bit streams arranged as a single serial bit stream of digital bits and having separately encoded pairs of control codes and corresponding data carried in the serial bit stream. The pipeline system employs a plurality of interconnected stages to decode and decompress the single bit stream, including a start code detector. When in a search mode, the start code detector searches for a specific start code corresponding to one of multiple compression standards. The start code detector responding to the single serial bit stream generates control tokens and data tokens. A respective one of the tokens includes a plurality of data words. Each data word has an extension bit which indicates a presence of additional words therein. The data words are thereby unlimited in number. A token decode circuit positioned in certain of the stages recognizes certain of the tokens as control tokens pertinent to that stage and passes unrecognized control tokens to a succeeding stage. A reconfigurable decode and parser processing means positioned in certain of the stages is responsive to a recognized control token and reconfigures a particular stage to handle an identified data token. Methods relating to the decoder and decompression system include processing steps relating thereto

[0001] This is a continuation-in-part application to U.S. Serial No.(not yet known) filed Feb. 2, 1995, which is a continuation applicationof Ser. No. 08/082,291 filed Jun. 24, 1993. This application claimspriority from EPO Application No. 92306038.8 filed Jun. 30, 1992,British Application No. 9405914.4 filed Mar. 24, 1994 and BritishApplication No. (not yet known) filed Feb. 28, 1995.

BACKGROUND OF THE INVENTION

[0002] The present invention is directed to improvements in methods andapparatus for decompression which operates to decompress and/or decode aplurality of differently encoded input signals. The illustrativeembodiment chosen for description hereinafter relates to the decoding ora Plurality of encoded picture standards. More specifically, thisembodiment relates to the decoding or any one of the well knownstandards known as JPEG, MPEG and MH.261.

[0003] A serial pipeline processing system of the present inventioncomprises a single two-wire bus used for carrying unique and specializedinteractive interfacing tokens, in the form or control tokens and datatokens, to a plurality of adaptive decompression circuits and the likepositioned as a reconfigurable pipeline processor.

[0004] Video compression/decompression systems are generally well-knownin the art. However, such systems have generally seen dedicated indesign and use to a single compression standard. They have also sufferedfrom a number or other inefficiencies and inflexibility in overallsystem and subsystem design and data flow management.

[0005] Examples of prior art systems and subsystems are enumerated asfollows:

[0006] One prior art system is described in U.S. Pat. No. 5,216,724. Theapparatus comprises a plurality of compute modules, in a preferredembodiment, for a total of four compute modules coupled in parallel.Each of the compute modules has a processor, dual port memory,scratch-pad memory, and an arbitration mechanism. A first bus couplesthe compute modules and a host processor. The device comprises a sharedmemory which is coupled to the host processor and to the compute moduleswith a second bus.

[0007] U.S. Pat. No. 4,785,349 discloses a full motion color digitalvideo signal that is compressed, formatted for transmission, recorded oncompact disc media and decoded at conventional video frame rates. Duringcompression, regions of a frame are individually analyzed to selectoptimum fill coding methods specific to each region. Region decodingtime estimates are made to optimize compression thresholds. Regiondescriptive codes conveying the size and locations of the regions aregrouped together in a first segment of a data stream. Region fill codesconveying pixel amplitude indications for the regions are groupedtogether according to fill code type and placed in other segments of thedata stream. The data stream segments are individually variable lengthcoded according to their respective statistical distributions andformatted to form data frames. The number of bytes per frame is witheredby the addition of auxiliary data determined by a reverse frame sequenceanalysis to provide an average number selected to minimize pauses of thecompact disc during playback, thereby avoiding unpredictable seek modelatency periods characteristic of compact discs. A decoder includes avariable length decoder responsive to statistical information in thecode stream for separately variable length decoding individual segmentsof the data stream. Region location data is derived from regiondescriptive data and applied with region fill codes to a plurality ofregion specific decoders selected by detection of the fill code type(e.g., relative, absolute, dyad and DPCM) and decoded region pixels arestored in a bit map for subsequent display.

[0008] U.S. Pat. No. 4,922,341 discloses a method forscene-model-assisted reduction of image data for digital televisionsignals, whereby a picture signal supplied at time is to be coded,whereby a predecessor frame from a scene already coded at time t-1 ispresent in an image store as a reference, and whereby the frame-to-frameinformation is composed of an amplification factor, a shift factor, andan adaptively acquired quad-tree division structure. Upon initializationof the system, a uniform, prescribed gray scale value or picturehalf-tone expressed as a defined luminance value is written into theimage store of a coder at the transmitter and in the image store of adecoder at the receiver store, in the same way for all picture elements(pixels). Both the image store in the coder as well as the image storein the decoder are each operated with feed back to themselves in amanner such that the content of the image store in the coder and decodercan be read out in blocks of variable size, can be amplified with afactor greater than or less than 1 of the luminance and can be writtenback into the image store with shifted addresses, whereby the blocks ofvariable size are organized according to a known quad tree datastructure.

[0009] U.S. Pat. No. 5,122,875 discloses an apparatus forencoding/decoding an HDTV signal. The apparatus includes a compressioncircuit responsive to high definition video source signals for providinghierarchically layered codewords CW representing compressed video dataand associated codewords T, defining the types of data represented bythe codewords CW. A priority selection circuit, responsive to thecodewords CW and T, parses the codewords CW into high and low prioritycodeword sequences wherein the high and low priority codeword sequencescorrespond to compressed video data of relatively greater and lesserimportance to image reproduction respectively. A transport processor,responsive to the high and low priority codeword sequences, forms highand low priority transport blocks of high and low priority codewords,respectively. Each transport block includes a header, codewords CW anderror detection check bits. The respective transport blocks are appliedto a forward error check circuit for applying additional error checkdata. Thereafter, the high and low priority data are applied to a modemwherein quadrature amplitude modulates respective carriers fortransmission.

[0010] U.S. Pat. No. 5,146,325 discloses a video decompression systemfor decompressing compressed image data wherein odd and even fields ofthe video signal are independently compressed in sequences of intraframeand interframe compression modes and then interleaved for transmission.The odd and even fields are independently decompressed. During intervalswhen valid decompressed odd/even field data is not available, even/oddfield data is substituted for the unavailable odd/even field data.Independently decompressing the even and odd fields of data andsubstituting the opposite field of data for unavailable data may be usedto advantage to reduce image display latency during system start-up andchannel changes.

[0011] U.S. Pat. No. 5,168,356 discloses a video signal encoding systemthat includes apparatus for segmenting encoded video data into transportblocks for signal transmission. The transport block format enhancessignal recovery at the receiver by virtue of providing header data fromwhich a receiver can determine re-entry points into the data stream onthe occurrence of a loss or corruption of transmitted data. The re-entrypoints are maximized by providing secondary transport headers embeddedwithin encoded video data in respective transport blocks.

[0012] U.S. Pat. No. 5,168,375 discloses a method for processing a fieldof image data samples to provide for one or more of the functions ofdecimation, interpolation, and sharpening. This is accomplished by anarray transform processor such as that employed in a JPEG compressionsystem. Blocks of data samples are transformed by the discrete evencosine transform (DECT) in both the decimation and interpolationprocesses, after which the number of frequency terms is altered. In thecase of decimation, the number of frequency terms is reduced, this beingfollowed by inverse transformation to produce a reduced-size matrix ofsample points representing the original block of data. In the case ofinterpolation, additional frequency components of zero value areinserted into the array of frequency components after which inversetransformation produces an enlarged data sampling set without anincrease in spectral bandwidth. In the case of sharpening, accomplishedby a convolution or filtering operation involving multiplication oftransforms of data and filter kernel in the frequency domain, there isprovided an inverse transformation resulting in a set of blocks ofprocessed data samples. The blocks are overlapped followed by a savingsof designated samples, and a discarding of excess samples from regionsof overlap. The spatial representation of the kernel is modified byreduction of the number of components, for a linear-phase filter, andzero-padded to equal the number of samples of a data block, this beingfollowed by forming the discrete odd cosine transform (DOCT) of thepadded kernel matrix.

[0013] U.S. Pat. No. 5,175,617 discloses a system and method fortransmitting logmap video images through telephone line band-limitedanalog channels. The pixel organization in the logmap image is designedto match the sensor geometry of the human eye with a greaterconcentration of pixels at the center. The transmitter divides thefrequency band into channels, and assigns one or two pixels to eachchannel, for example a 3 KHz voice quality telephone line is dividedinto 768 channels spaced about 3.9 Hz apart. Each channel consists oftwo carrier waves in quadrature, so each channel can carry two pixels.Some channels are reserved for special calibration signals enabling thereceiver to detect both the phase and magnitude of the received signal.If the sensor and pixels are connected directly to a bank of oscillatorsand the receiver can continuously receive each channel, then thereceiver need not be synchronized with the transmitter. An FFT algorithmimplements a fast discrete approximation to the continuous case in whichthe receiver synchronizes to the first frame and then acquiressubsequent frames every frame period. The frame period is relatively lowcompared with the sampling period so the receiver is unlikely to loseframe synchrony once the first frame is detected. An experimental videotelephone transmitted 4 frames per second, applied quadrature coding to1440 pixel logmap images and obtained an effective data transfer rate inexcess of 40,000 bits per second.

[0014] U.S. Pat. No. 5,185,819 discloses a video compression systemhaving odd and even fields of video signal that are independentlycompressed in sequences of intraframe and interframe compression modes.The odd and even fields of independently compressed data are interleavedfor transmission such that the intraframe even field compressed dataoccurs midway between successive fields of intraframe odd fieldcompressed data. The interleaved sequence provides receivers with twicethe number of entry points into the signal for decoding withoutincreasing the amount of data transmitted.

[0015] U.S. Pat. No. 5,212,742 discloses an apparatus and method forprocessing video data for compression/decompression in real-time. Theapparatus comprises a plurality of compute modules, in a preferredembodiment, for a total of four compute modules coupled in parallel.Each of the compute modules has a processor, dual port memory,scratch-pad memory, and an arbitration mechanism. A first bus couplesthe compute modules and host processor. Lastly, the device comprises ashared memory which is coupled to the host processor and to the computemodules with a second bus. The method handles assigning portions of theimage for each of the processors to operate upon.

[0016] U.S. Pat. No. 5,231,484 discloses a system and method forimplementing an encoder suitable for use with the proposed ISO/IEC MPEGstandards. Included are three cooperating components or subsystems thatoperate to variously adaptively pre-process the incoming digital motionvideo sequences, allocate bits to the pictures in a sequence, andadaptively quantize transform coefficients in different regions of apicture in a video sequence so as to provide optimal visual qualitygiven the number of bits allocated to that picture.

[0017] U.S. Pat. No. 5,267,334 discloses a method of removing frameredundancy in a computer system for a sequence of moving images. Themethod comprises detecting a first scene change in the sequence ofmoving images and generating a first keyframe containing complete sceneinformation for a first image. The first keyframe is known, in apreferred embodiment, as a “forward-facing” keyframe or intraframe, andit is normally present in CCITT compressed video data. The process thencomprises generating at least one intermediate compressed frame, the atleast one intermediate compressed frame containing differenceinformation from the first image for at least one image following thefirst image in time in the sequence of moving images. This at least oneframe being known as an interframe. Finally, detecting a second scenechange in the sequence of moving images and generating a second keyframecontaining complete scene information for an image displayed at the timejust prior to the second scene change, known as a “backward-facing”keyframe. The first keyframe and the at least one intermediatecompressed frame are linked for forward play, and the second keyframeand the intermediate compressed frames are linked in reverse for reverseplay. The intraframe may also be used for generation of complete sceneinformation when the images are played in the forward direction. Whenthis sequence is played in reverse, the backward-facing keyframe is usedfor the generation of complete scene information.

[0018] U.S. Pat. No. 5,276,513 discloses a first circuit apparatus,comprising a given number of prior-art image-pyramid stages, togetherwith a second circuit apparatus, comprising the same given number ofnovel motion-vector stages, perform cost-effective hierarchical motionanalysis (HeMA) in real-time, with minimum system processing delayand/or employing minimum system processing delay and/or employingminimum hardware structure. Specifically, the first and second circuitapparatus, in response to relatively high-resolution image data from anongoing input series of successive given pixel-density image-data framesthat occur at a relatively high frame rate (e.g., 30 frames per second),derives, after a certain processing-system delay, an ongoing outputseries of successive given pixel-density vector-data frames that occurat the same given frame rate. Each vector-data frame is indicative ofimage motion occurring between each pair of successive image frames.

[0019] U.S. Pat. No. 5,283,646 discloses a method and apparatus forenabling a real-time video encoding system to accurately deliver thedesired number of bits per frame, while coding the image only once,updates the quantization step size used to quantize coefficients whichdescribe, for example, an image to be transmitted over a communicationschannel. The data is divided into sectors, each sector including aplurality of blocks. The blocks are encoded, for example, using DCTcoding, to generate a sequence of coefficients for each block. Thecoefficients can be quantized, and depending upon the quantization step,the number of bits required to describe the data will varysignificantly. At the end of the transmission of each sector of data,the accumulated actual number of bits expended is compared with theaccumulated desired number of bits expended, for a selected number ofsectors associated with the particular group of data. The system thenreadjusts the quantization step size to target a final desired number ofdata bits for a plurality of sectors, for example describing an image.Various methods are described for updating the quantization step sizeand determining desired bit allocations.

[0020] The article, Chong, Yong M., A Data-Flow Architecture for DigitalImage Processing, Wescon Technical Papers: No. 2 October/November 1984,discloses a real-time signal processing system specifically designed forimage processing. More particularly, a token based data-flowarchitecture is disclosed wherein the tokens are of a fixed one wordwidth having a fixed width address field. The system contains aplurality of identical flow processors connected in a ring fashion. Thetokens contain a data field, a control field and a tag. The tag field ofthe token is further broken down into a processor address field and anidentifier field. The processor address field is used to direct thetokens to the correct data-flow processor, and the identifier field isused to label the data such that the data-flow processor knows what todo with the data. In this way, the identifier field acts as aninstruction for the data-flow processor. The system directs each tokento a specific data-flow processor using a module number (MN). If the MNmatches the MN of the particular stage, then the appropriate operationsare performed upon the data. If unrecognized, the token is directed toan output data bus.

[0021] The article, Kimori, S. et al. An Elastic Pineline Mechanism bySelf-Timed Circuits, IEEE J. of Solid-State Circuits, Vol. 23, No. 1,February 1988, discloses an elastic pipeline having self-timed circuits.The asynchronous pipeline comprises a plurality of pipeline stages. Eachof the pipeline stages consists of a group of input data latchesfollowed by a combinatorial logic circuit that carries out logicoperations specific to the pipeline stages. The data latches aresimultaneously supplied with a triggering signal generated by adata-transfer control circuit associated with that stage. Thedata-transfer control circuits are interconnected to form a chainthrough which send and acknowledge signal lines control a hand-shakemode of data transfer between the successive pipeline stages.Furthermore, a decoder is generally provided in each stage to selectoperations to be done on the operands in the present stage. It is alsopossible to locate the decoder in the preceding stage in order topre-decode complex decoding processing and to alleviate critical pathproblems in the logic circuit. The elastic nature of the pipelineeliminates any centralized control since all the interworkings betweenthe submodules are determined by a completely localized decision and, inaddition, each submodule can autonomously perform data buffering andself-timed data-transfer control at the same time. Finally, to increasethe elasticity of the pipeline, empty stages are interleaved between theoccupied stages in order to ensure reliable data transfer between thestages.

[0022] U.S. Pat. No. 5,278,646 discloses an improved technique fordecoding wherein the number of coefficients to be included in eachsub-block is selectable, and a code indicating the number ofcoefficients within each layer is inserted in the bitstream at thebeginning of each encoded video sequence. This technique allows theoriginal runs of zero coefficients in the highest resolution layer toremain intact by forming a sub-block for each scale from a selectednumber of coefficients along a continuous scan. These sub-blocks may bedecoded in a standard fashion, with an inverse discrete cosine transformapplied to square sub-blocks obtained by the appropriate zero padding ofand/or discarding of excess coefficients from each of the scales. Thistechnique further improves decoding efficiency by allowing an implicitend of block signal to separate blocks, making it unnecessary to decodean explicit end of block signal in most cases.

[0023] U.S. Pat. No. 4,903,018 discloses a process and data processingsystem for compressing and expanding structurally associated multipledata sequences. The process is particular to data sets in which ananalysis is made of the structure in order to identify a characteristiccommon to a predetermined number of successive data elements of a datasequence. In place of data elements, a code as used which is againdecoded during expansion. The common characteristic is obtained byanalyzing data elements which have the same order number in a number ofdata sequences. During expansion, the data elements obtained by decodingthe code are ordered in data series on the basis of the order number ofthese data series on the basis of the order number of these dataelements. The data processing system for performing the processesincludes a storage matrix (26) and an index storage (28) having lineaddresses of the storage matrix (26) in an assorted line sequence.

[0024] U.S. Pat. No. 4,334,246 discloses a circuit and method fordecompressing video subsequent to its prior compression for transmissionor storage. The circuit assumes that the original video generated by araster input scanner was operated on by a two line one shot predictor,coded using run length encoding into code words of four, eight or twelvebits and packed into sixteen bit data words. This describeddecompressor, then, unpacks the data by joining together the sixteen bitdata words and then separately the individual code words, converts thecode words into a number of all zero four bit nibbles and a terminatingnibble containing one or more one bits which constitutes decoded data,inspects the actual video of the preceding scan line and the previousvideo bits of the present line to produce depredictor bits and comparesthe decoded data and depredictor bits to produce the final actual video.

[0025] U.S. Pat. No. 5,060,242 discloses an image signal processingsystem DPCM encodes the signal, then Huffman and run length encodes thesignal to produce variable length code words, which are then tightlypacked without gaps for efficient transmission without loss of any data.The tightly packed apparatus has a barrel shifter with its shift moduluscontrolled by an accumulator receiving code word length information. AnOR gate is connected to the shifter, while a register is connected tothe gate. Apparatus for processing a tightly packed and decorrelateddigital signal has a barrel shifter and accumulator for unpacking, aHuffman and run length decoder, and an inverse DCPM decoder.

[0026] U.S. Pat. No. 5,168,375 discloses a method for processing a fieldof image data samples to provide for one or more of the functions ofdecimation, interpolation, and sharpening is accomplished by use of anarray transform processor such as that employed in a JPEG compressionsystem. Blocks of data samples are transformed by the discrete evencosine transform (DECT) in both the decimation and interpolationprocesses, after which the number of frequency terms is altered. In thecase of decimation, the number of frequency terms is reduced, this beingfollowed by inverse transformation to produce a reduced-size matrix ofsample points representing the original block of data. In the case ofinterpolation, additional frequency components of zero value areinserted into the array of frequency components after which inversetransformation produces an enlarged data sampling set without anincrease in spectral bandwidth. In the case of sharpening, accomplishedby a convolution or filtering operation involving multiplication oftransforms of data and filter kernel in the frequency domain, there isprovided an inverse transformation resulting in a set of blocks ofprocessed data samples. The blocks are overlapped followed by a savingsof designated samples, and a discarding of excess samples from regionsof overlap. The spatial representation of the kernel is modified byreduction of the number of components, for a linear-phase filter, andzero-padded to equal the number of samples of a data block, this beingfollowed by forming the discrete odd cosine transform (DOCT) of thepadded kernel matrix.

[0027] U.S. Pat. No. 5,231,486 discloses a high definition video systemprocesses a bitstream including high and low priority variable lengthcoded Data words. The coded Data is separated into packed High PriorityData and packed Low Priority Data by means of respective data packingunits. The coded Data is continuously applied to both packing units.High Priority and Low Priority Length words indicating the bit lengthsof high priority and low priority components of the coded Data areapplied to the high and low priority data packers, respectively. The LowPriority Length word is zeroed when high Priority Data is to be packedfor transport via a first output path, and the High Priority Length wordis zeroed when Low Priority Data is to be packed for transport via asecond output path.

[0028] U.S. Pat. No. 5,287,178 discloses a video signal encoding systemincludes a signal processor for segmenting encoded video data intotransport blocks having a header section and a packed data section. Thesystem also includes reset control apparatus for releasing resets ofsystem components, after a global system reset, in a prescribednon-simultaneous phased sequence to enable signal processing to commencein the prescribed sequence. The phased reset release sequence beginswhen valid data is sensed as transmitting the data lines.

[0029] U.S. Pat. No. 5,124,790 to Nakayama discloses a reverse quantizerto be used with image memory. The inverse quantizer is used in thestandard way to decode differential predictive coding method (DPCM)encoded data.]

[0030] U.S. Pat. No. 5,136,371 to Savatier et al. is directed to ade-quantizer having an adjustable quantizational level which is variableand determined by the fullness of the buffer. The applicants state thatthe novel aspect of their invention is the maximum available data ratethat is achieved. Buffer overflow and underflow is avoided by adaptingthe quantization step size the quantizer 152 and the de-quantizer 156 bymeans of a quantizational level which is recalculated after each blockhas been encoded. The quantization level is calculated as a function ofthe amount of already encoded data for the frame, compared with thetotal buffer size. In this manner, the quantization level canadvantageously be recalculated by the decoder and does not have to betransmitted.

[0031] U.S. Pat. No. 5,142,380 to Sakagami et al. discloses an imagecompression apparatus suitable for use with still images such as thoseformed by electronic still cameras using solid state image sensors. Thequantizer employed is connected to a memory means from which thresholdvalues of a quantization matrix for the laminate signal, Y, and rom 15stores threshold values of a quantization matrix for the crominantsignals I and Q.

[0032] U.S. Pat. No. 5,193,002 to Guichard et al. disclosed an apparatusfor coding/decoding image signals in real time in conjunction with theCCITT standard H.261. A digital signal processor carries out directquantization and reverse quantization.

[0033] U.S. Pat. No. 5,241,383 to Chen et al. describes an apparatuswith a pseudo-constant bit rate video coding achieved by an adjustablequantization parameter. The qunatization parameter utilized by thequantizer 32 is periodically adjusted to increase or decrease the amountof code bits generated by the coding circuit. The change in quantizationparameters for coding the next group of pictures is determined by adeviation measure between the actual number of code bits generated bythe coding circuits for the previous group of pictures in an estimatenumber of code bits for the previous group of pictures. The number ofcode bits generated by the coding circuit is controlled by controllingthe quantizer step sizes. In general smaller quantizer step sizes resultin more code bits in larger quantizer step sizes result in fewer codebits.

[0034] U.S. Pat. No. 5,113,255 to Nagata et al; U.S. Pat. No. 5,126,842to Andrews et al; U.S. Pat. No. 5,253,058 to Gharavi; U.S. Pat. No.5,260,782 to Hui; and U.S. Pat. No. 5,212,742 to Normile et al areincluded for background and as a general description of the art.

[0035] Accordingly, those concerned with the design, development and useof video compression/decompression systems and related subsystems havelong recognized a need for improved methods and apparatus providingenhanced flexibility, efficiency and performance. The present inventionclearly fulfills all these needs.

SUMMARY OF THE INVENTION

[0036] Briefly, and in general terms, the present invention provides aninput, an output and a plurality of processing stages between the inputand the output, the plurality of processing stages being interconnectedby a two-wire interface for conveyance of tokens along a pipeline, andcontrol and/or DATA tokens in the form of universal adaptation units forinterfacing with all of the stages in the pipeline and interacting withselected stages in the pipeline for control, data and/or combinedcontrol-data functions among the processing stages, whereby theprocessing stages in the pipeline are afforded enhanced flexibility inconfiguration and processing.

[0037] Each of the processing stages in the pipeline may include bothprimary and secondary storage, and the stages in the pipeline arereconfigurable in response to recognition of selected tokens. The tokensin the pipeline are dynamically adaptive and may be position dependentupon the processing stages for performance of functions or positionindependent of the processing stages for performance of functions.

[0038] In a pipeline machine, in accordance with the invention, thetokens may be altered by interfacing with the stages, and the tokens mayinteract with all of the processing stages in the pipeline or only withsome but less than all of said processing stages. The tokens in thepipeline may interact with adjacent processing stages or withnon-adjacent processing stages, and the tokens may reconfigure theprocessing stages. Such tokens may be position dependent for somefunctions and position independent for other functions in the pipeline.

[0039] The tokens, in combination with the reconfigurable processingstages, provide a basic building block for the pipeline system. Theinteraction of the tokens with a processing stage in the pipeline may beconditioned by the previous processing history of that processing stage.The tokens may have address fields which characterize the tokens, andthe interactions with a processing stage may be determined by suchaddress fields.

[0040] In an improved pipeline machine, in accordance with theinvention, the tokens may include an extension bit for each token, theextension bit indicating the presence of additional words in that tokenand identifying the last word in that token. The address fields may beof variable length and may also be Huffman coded.

[0041] In the improved pipeline machine, the tokens may be generated bya processing stage. Such pipeline tokens may include data for transferto the processing stages or the tokens may be devoid of data. Some ofthe tokens may be identified as DATA tokens and provide data to theprocessing stages in the pipeline, while other tokens are identified ascontrol tokens and only condition the processing stages in the pipeline,such conditioning including reconfiguring of the processing stages.Still other tokens may provide both data and conditioning to theprocessing stages in the pipeline. Some of said tokens may identifycoding standards to the processing stages in the pipeline, whereas othertokens may operate independent of any coding standard among theprocessing stages. The tokens may be capable of successive alteration bythe processing stages in the pipeline.

[0042] In accordance with the invention, the interactive flexibility ofthe tokens in cooperation with the processing stages facilitates greaterfunctional diversity of the processing stages for resident structure inthe pipeline, and the flexibility of the tokens facilitates systemexpansion and/or alteration. The tokens may be capable of facilitating aplurality of functions within any processing stage in the pipeline. Suchpipeline tokens may be either hardware based or software based. Hence,the tokens facilitate more efficient uses of system bandwidth in thepipeline. The tokens may provide data and control simultaneously to theprocessing stages in the pipeline.

[0043] The invention may include a pipeline processing machine forhandling plurality of separately encoded bit streams arranged as asingle serial bit stream of digital bits and having separately encodedpairs of control codes and corresponding data carried in the serial bitstream and employing a plurality of stages interconnected by a two-wireinterface, further characterized by a start code detector responsive tothe single serial bit stream for generating control tokens and DATAtokens for application to the two-wire interface, a token decode circuitpositioned in certain of the stages for recognizing certain of thetokens as control tokens pertinent to that stage and for passingunrecognized control tokens along the pipeline, and a reconfigurabledecode and parser processing means responsive to a recognized controltoken for reconfiguring a particular stage to handle an identified DATAtoken.

[0044] The pipeline machine may also include first and second registers,the first register being positioned as an input of the decode and parsermeans, with the second register positioned as an output of the decodeand parser means. One of the processing stages may be a spatial decoder,a second of the stages being a token generator for generating controltokens and DATA tokens for passage along the two-wire interface. A tokendecode means is positioned in the spatial decoder for recognizingcertain of the tokens as control tokens pertinent to the spatial decoderand for configuring the spatial decoder for spatially decoding DATAtokens following a control token into a first decoded format.

[0045] A further stage may be a temporal decoder positioned downstreamin the pipeline from the spatial decoder, with a second token decodemeans positioned in the temporal decoder for recognizing certain of thetokens as control tokens pertinent to the temporal decoder and forconfiguring the temporal decoder for termporally decoding the DATAtokens following the control token into a first decoded format. Thetemporal decoder may utilize a reconfigurable prediction filter which isreconfigurable by a prediction token.

[0046] Data may be moved along the two-wire interface within thetemporal decoder in 8×8 pel data blocks, and address means may beprovided for storing and retrieving such data blocks along blockboundaries. The address means may store and retrieve blocks of dataacross block boundaries. The address means reorders said blocks aspicture data for display. The data blocks stored and retrieved may begreater and/or smaller than 8×8 pel data blocks. Circuit means may alsobe provided for either displaying the output of the temporal decoder orwriting the output back into a picture memory location. The decodedformat may be either a still picture format or a moving picture format.

[0047] The processing stage may also include, in accordance with theinvention, a token decoder for decoding the address of a token and anaction identifier responsive to the token decoder to implementconfiguration of the processing stage. The processing stages reside in apipeline processing machine having a plurality of the processing stagesinterconnected by a two-wire interface bus, with control tokens and DATAtokens passing over the two-wire interface. A token decode circuit ispositioned in certain of the processing stages for recognizing certainof the tokens as control tokens pertinent to that stage and for passingunrecognized control tokens along the pipeline. A first input latchcircuit may be positioned on the two-wire interface preceding theprocessing stage and a second output latch circuit may be positioned onthe two-wire interface succeeding the processing stage. The token decodecircuit is connected to the two-wire interface through the first inputlatch. Predetermined processing stages may include a decoding circuitconnected to the output of a predetermined data storage device, wherebyeach processing stage assumes the active state only when the stagecontains a predetermined stage activation signal pattern and remains inthe activation mode until the stage contains a predetermined stagedeactivation pattern.

[0048] In accordance with the invention, one of the stages is a StartCode Detector for receiving the input and being adapted to generateand/or convert the tokens. The Start Code Detector is responsive to datato create tokens, searches for and detects start codes and producestokens in response thereto, and is capable of detecting overlappingstart codes, whereby the first start code is ignored and the secondstart code is used to create start code tokens.

[0049] The Start Code Detector stage is adapted to search an input datastream in a search mode for a selected start code. The detector searchesfor breaks in the data stream, and the search may be made of data froman external data source. The Start Code Detector stage may produce aSTART CODE token, a PICTURE_START token, a SLICE_START token, aPICTURE_END token, a SEQUENCE_START token, a SEQUENCE_END token, and/ora GROUP_START token. The Start Code Detector stage may also perform apadding function by adding bits to the last word of a token.

[0050] The Start Code Detector may provide, in a machine for handling aplurality of separately encoded bit streams arranged as a serial bitstream of digital bits and having separately encoded pairs of startcodes and data carried in the serial bit stream, a Start Code Detectorsubsystem having first, second and third registers connected in serialfashion, each of the registers storing a different number of bits fromthe bit stream, the first register storing a value, the second registerand a first decode means identifying a start code associated with thevalue contained in said first register. Circuit means shift the lattervalue to a predetermined end of the third register, and a second decodemeans is arranged for accepting data from the third register inparallel.

[0051] A memory may also be provided which is responsive to the seconddecode means for providing one or more control tokens stored in thememory as a result of the decoding of the value associated with thestart code. A plurality of tag shift registers may be provided forhandling tags indicating the validity of data from the registers. Thesystem may also include means for accessing the input data stream from amicroprocessor interface, and means for formatting and organizing thedata stream.

[0052] In accordance with the invention, the Start Code Detector mayidentify start codes of varying widths associated with differentlyencoded bit streams. The detector may generate a plurality of DATATokens from the input data stream. Further in accordance with theinvention, the system may be a pipeline system and the Start CodeDetector may be positioned as the first processing stage in thepipeline.

[0053] The present invention also provides, in a digital pictureinformation processing system, means for selectively configuring thesystem to process data in accordance with a plurality of differentpicture compression/decompression standards. The picture standards mayinclude JPEG, MPEG, and/or H.261, or any other standards and anycombination of such picture standards, without departing in any way fromthe spirit and scope of the invention. In accordance with the invention,the system may include a spatial decoder for video data and having aHuffman decoder, an index to data and an arithmetic logic unit with amicrocode ROM having separate stored programs for each of a plurality ofdifferent picture compression/decompression standards, such programsbeing selectable by an interfacing adaptation unit in the form of atoken, so that processing for a plurality of picture standards isfacilitated. A multi-standard system in accordance with the invention,may utilize tokens for its operation regardless of the selected picturestandard, and the tokens may be utilized as a generic communicationprotocol in the system for all of the various picture standards. Thesystem may be further characterized by a multi-standard token formapping differently encoded data streams arranged on a single serialstream of data onto a single decoder using a mixture of standarddependent and standard independent hardware and control tokens. Thesystem may also include an address generation means for arrangingmacroblocks of data associated with different picture standards into acommon addressing scheme.

[0054] The present invention also provides, in a system having aplurality of processing stages, a universal adaptation unit in the formof an interactive interfacing token for control and/or data functionsamong the processing stages, the token being a PICTURE_START code tokenfor indicating that the start of a picture will follow in the subsequentDATA token.

[0055] The token may also be a PICTURE_END token for indicating the endof an individual picture.

[0056] The token may also be a FLUSH token for clearing buffers andresetting the system as it proceeds down the system from the input tothe output. In accordance with the invention, the FLUSH token mayvariably reset the stages as the token proceeds down the pipeline.

[0057] The token may also be a CODING_STANDARD token for conditioningthe system for processing in a selected one of a plurality of picturecompression/decompression standards.

[0058] The CODING_STANDARD token may designate the picture standard asJPEG, and/or any other appropriate picture standard. At least some ofthe processing stages reconfigure in response to the CODING_STANDARDtoken.

[0059] One of the processing stages in the system may be a Huffmandecoder and parser and, upon receipt of a CODING_STANDARD control token,the parser is reset to an address location corresponding to the locationof a program for handling the picture standard identified by theCODING_STANDARD control token. A reset address may also be selected bythe CODING_STANDARD control token corresponding to a memory locationused for testing the Huffman decoder and parser.

[0060] The Huffman decoder may include a decoding stage and an Index toData stage, and the parser stage may send an instruction to the Index toData Unit to select tables needed for a particular identified codingstandard, the parser stage indicating whether the arriving data isinverted or not.

[0061] The aforedescribed tokens may take the form of an interactivemetamorphic interfacing token.

[0062] The present invention also provides a system for decoding videodata, having a Huffman decoder, an index to data (ITOD) stage, anarithmetic logic unit (ALU), and a data buffering means immediatelyfollowing the system, whereby time spread for video pictures of varyingdata size can be controlled.

[0063] The system may include a spatial decoder having a two-wireinterface interconnecting processing stages, the interface enablingserial processing for data and parallel processing for control.

[0064] As previously indicated, the system may further include a ROMhaving separate stored programs for each of a plurality of picturestandards, the programs being selectable by a token to facilitateprocessing for a plurality of different picture standards. The spatialdecoder system also includes a token formatter for formatting tokens, sothat DATA tokens are created.

[0065] The system may also include a decoding stage and a parser stagefor sending an instruction to the Index to Data Unit to select tablesneeded for a particular identified coding standard, the parser stageindicating whether the arriving data is inverted or not. The tables maybe arranged within a memory for enabling multiple use of the tableswhere appropriate.

[0066] The present invention also provides a pipeline system having aninput data stream, and a processing stage for receiving the input datastream, the stage including means for recognizing specified bit streampatterns, whereby said stage facilitates random access and errorrecovery. In accordance with the invention, the processing stage may bea start code detector and the bit stream patterns may include startcodes. Hence, the invention provides a search-mode means for searchingdifferently encoded data streams arranged as a single serial stream ofdata for allowing random access and enhanced error recovery.

[0067] The present invention also provides a pipeline machine havingmeans for performing a stop-after-picture operation for achieving aclear end to picture data decoding, for indicating the end of a picture,and for clearing the pipeline, wherein such means generates acombination of a PICTURE_END token and a FLUSH token.

[0068] The present invention also provides, in a pipeline machine, afixed size, fixed width buffer and means for padding the buffer to passan arbitrary number of bits through the buffer. The padding means may bea start code detector.

[0069] Padding may be performed only on the last word of a token andpadding insures uniformity of word size. In accordance with theinvention, a reconfigurable processing stage may be provided as aspatial decoder and the padding means adds to picture data being handledby the spatial decoder sufficent additional bits such that eachdecompressed picture at the output of the spatial decoder is of the samelength in bits.

[0070] The present invention also provides, in a system having a datastream including run length code, an inverse modeller means active uponthe data stream from a token for expending out the run level code to arun of zero data followed by a level, whereby each token is expressedwith a specified number of values. The token may be a DATA token.

[0071] The inverse modeller means blocks tokens which lack the specifiednumber of values, and the specified number of values may be 64coefficients in a presently preferred embodiment of the invention.

[0072] The practice of the invention may include an expanding circuitfor accepting a DATA token having run length codes and decoding the runlength codes. A padder circuit in communication with the expandingcircuit checks that the DATA token has a predetermined length so that ifthe DATA token has less than the predetermined length, the paddercircuit adds units of data to the DATA token until the predeterminedlength is achieved. A bypass circuit is also provided for bypassing anytoken other than a DATA token around the expanding circuit and thepadding circuit.

[0073] In accordance with the invention, a method is provided for datato efficiently fill a buffer, including providing first type tokenshaving a first predetermined width, and at least one of the followingformats:

[0074] Format A—ExxxxxxLLLLLLLLLLL

[0075] Format B×ERRRRRRLLLLLLLLLLL

[0076] Format C×E000000LLLLLLLLLLL

[0077] where E=extention bit; F=specifics format; R=run bit; L=lengthbit or non-data token; x=“don't care” bit, splitting format A tokensinto a format Oa token having a form of ELLLLLLLLLLL, splitting format Btokens into a format 1 token having the form of FRRRRRROOOOO and aformat 0 a data token, splitting format C tokens into a format 0 tokenhaving the form of FLLLLLLLLLLL, and packing format 0, format 0 a andformat 1 tokens into a buffer, having a second predetermined width.

[0078] The invention also provides an apparatus for providing a timedelay to a group of compressed pictures, the pictures corresponding to avideo compression/decompression standard, wherein words of datacontaining compressed pictures are counted by a counter circuit and amicroprocessor, in communication with the counter circuit and adapted toreceive start-up information consistent with the standard of videodecompression, communicates the start-up information to the countercircuit.

[0079] An inverse modeller circuit, for accepting the words of data andcapable of delaying the words of data, is in communication with acontrol circuit intermediate the counter circuit and the inversemodeller circuit, the control circuit also communicating with thecounter circuit which compares the start-up information with the countedwords of data and signals the control circuit. The control circuitqueues the signals in correspondence to the words of data that have metthe start-up criterion and controls the inverse modeller delay feature.

[0080] The present invention also provides in a pipeline system havingan inverse modeller stage and an inverse discrete cosine transformstage, the improvement characterized by a processing stage, positionedbetween the inverse modeller stage and the inverse discrete cosinetransform stage, responsive to a token table for processing data.

[0081] In accordance with the invention, the token may be a QUANT_TABLEtoken for causing the processing stage to generate a quantization table.

[0082] The present invention also provides a Huffman decoder fordecoding data words encoded according to the Huffman coding provisionsof either H.261, JPEG or MPEG standards, the data words including anidentifier that identifies the Huffman code standard under which thedata words were coded, and comprising means for receiving the Huffmancoded data words, means for reading the identifier to determine whichstandard governed the Huffman coding of the received data words, meansfor converting the data words to JPEG Huffman coded data words, ifnecessary, in response to reading the identifier that identifies theHuffman coded data words as H.261 or MPEG Huffman coded, means operablyconnected to the Huffman coded data words receiving means for generatingan index number associated with each JPEG Huffman coded data wordreceived from the Huffman coded data words receiving means, and meansfor operating a lookup table containing a Huffman code table having theformat used under the JPEG standard to transmit JPEG Huffman tableinformation, including an input for receiving an index number from theindex number generating means, and including an output that is a decodeddata word corresponding to the index number.

[0083] The invention further relates, in varying degrees of scope, to amethod for decoding data words encoded according to the Huffman codingprovisions of either H.261, JPEG or MPEG standards, the data wordsincluding an identifier that identifies the Huffman code standard underwhich the data words were coded, such steps comprising receiving theHuffman coded data words, including reading the identifier to determinewhich standard governed the Huffman coding of the received data words,if necessary, in response to reading the identifier that identifies theHuffman coded data words as H.261 or MPEG Huffman coded, generating anindex number associated with each JPEG Huffman coded data word received,operating a lookup table containing a Huffman code table having theformat used under the JPEG standard to transmit JPEG Huffman tableinformation, including receiving an index number, and generating adecoded data word corresponding to the received index number.

[0084] The above and other objectives and advantages of the inventionwill become apparent from the following more detailed description whentaken in conjunction with the accompanying drawings.

DESCRIPTION OF THE DRAWINGS

[0085]FIG. 1 illustrates six cycles of a six-stage pipeline fordifferent combinations of two internal control signals;

[0086]FIGS. 2a and 2 b illustrate a pipeline in which each stageincludes auxiliary data storage. They also show the manner in whichpipeline stages can “compress” and “expand” in response to delays in thepipeline;

[0087]FIGS. 3a(1), 3 a(2), 3 b(1) and 3 b(2) illustrate the control ofdata transfer between stages of a preferred embodiment of a pipelineusing a two-wire interface and a multi-phase clock;

[0088]FIG. 4 is a block diagram that illustrates a basic embodiment of apipeline stage that incorporates a two-wire transfer control and alsoshows two consecutive pipeline processing stages with the two-wiretransfer control;

[0089]FIGS. 5a and 5 b taken together depict one example of a timingdiagram that shows the relationship between timing signals, input andoutput data, and internal control signals used in the pipeline stage asshown in FIG. 4;

[0090]FIG. 6 is a block diagram of one example of a pipeline stage thatholds its state under the control of an extension bit;

[0091]FIG. 7 is a block diagram of a pipeline stage that decodes stageactivation data words;

[0092]FIGS. 8a and 8 b taken together form a block diagram showing theuse of the two-wire transfer control in an exemplifying “dataduplication” pipeline stage;

[0093]FIGS. 9a and 9 b taken together depict one example of a timingdiagram that shows the two-phase clock, the two-wire transfer controlsignals and the other internal data and control signals used in theexemplifying embodiment shown in FIGS. 8a and 8 b.

[0094]FIG. 10 is a block diagram of a reconfigurable processing stage;

[0095]FIG. 11 is a block diagram of a spatial decoder;

[0096]FIG. 12 is a block diagram of a temporal decoder;

[0097]FIG. 13 is a block diagram of a video formatter;

[0098]FIGS. 14a-c show various arrangements of memory blocks used in thepresent invention:

[0099]FIG. 14a is a memory map showing a first arrangement ofmacroblocks;

[0100]FIG. 14b is a memory map showing a second arrangement ofmacroblocks;

[0101]FIG. 14c is a memory map showing a further arrangement ofmacroblocks;

[0102]FIG. 15 shows a Venn diagram of possible table selection values;

[0103]FIG. 16 shows the variable length of picture data used in thepresent invention;

[0104]FIG. 17 is a block diagram of the temporal decoder including theprediction filters;

[0105]FIG. 18 is a pictorial representation of the prediction filteringprocess;

[0106]FIG. 19 shows a generalized representation of the macroblockstructure;

[0107]FIG. 20 shows a generalized block diagram of a Start CodeDetector;

[0108]FIG. 21 illustrates examples of start codes in a data stream;

[0109]FIG. 22 is a block diagram depicting the relationship between theflag generator, decode index, header generator, extra word generator andoutput latches;

[0110]FIG. 23 is a block diagram of the Spatial Decoder DRAM interface;

[0111]FIG. 24 is a block diagram of a write swing buffer;

[0112]FIG. 25 is a pictorial diagram illustrating prediction data offsetfrom the block being processed;

[0113]FIG. 26 is a pictorial diagram illustrating prediction data offsetby (1,1);

[0114]FIG. 27 is a block diagram illustrating the Huffman decoder andparser state machine of the Spatial Decoder.

[0115]FIG. 28 is a block diagram illustrating the prediction filter.

[0116]FIG. 29 shows a typical decoder system;

[0117]FIG. 30 shows a JPEG still picture decoder;

[0118]FIG. 31 shows a JPEG video decoder;

[0119]FIG. 32 shows a multi-standard video decoder;

[0120]FIG. 33 shows the start and the end of a token;

[0121]FIG. 34 shows a token address and data fields;

[0122]FIG. 35 shows a token on an interface wider than 8 bits;

[0123]FIG. 36 shows a macroblock structure;

[0124]FIG. 37 shows a two-wire interface protocol;

[0125]FIG. 38 shows the location of external two-wire interfaces;

[0126]FIG. 39 shows clock propagation;

[0127]FIG. 40 shows two-wire interface timing;

[0128]FIG. 41 shows examples of access structure;

[0129]FIG. 42 shows a read transfer cycle;

[0130]FIG. 43 shows an access start timing;

[0131]FIG. 44 shows an example access with two write transfers;

[0132]FIG. 45 shows a read transfer cycle;

[0133]FIG. 46 shows a write transfer cycle;

[0134]FIG. 47 shows a refresh cycle;

[0135]FIG. 48 shows a 32 bit data bus and a 256 kbit deep DRAMs (9 bitrow address);

[0136]FIG. 49 shows timing parameters for any strobe signal;

[0137]FIG. 50 shows timing parameters between any two strobe signals;

[0138]FIG. 51 shows timing parameters between a bus and a strobe;

[0139]FIG. 52 shows timing parameters between a bus and a strobe;

[0140]FIG. 53 shows an MPI read timing;

[0141]FIG. 54 shows an MPI write timing;

[0142]FIG. 55 shows organization of large integers in the memory map;

[0143]FIG. 56 shows a typical decoder clock regime;

[0144]FIG. 57 shows input clock requirements;

[0145]FIG. 58 shows the Spatial Decoder;

[0146]FIG. 59 shows the inputs and outputs of the input circuit;

[0147]FIG. 60 shows the coded port protocol;

[0148]FIG. 61 shows the start code detector;

[0149]FIG. 62 shows start codes detected and converted to Tokens;

[0150]FIG. 63 shows the start codes detector passing Tokens;

[0151]FIG. 64 shows overlapping MPEG start codes (byte aligned);

[0152]FIG. 65 shows overlapping MPEG start codes (not byte aligned);

[0153]FIG. 66 shows jumping between two video sequences;

[0154]FIG. 67 shows a sequence of extra Token insertion;

[0155]FIG. 68 shows decoder start-up control;

[0156]FIG. 69 shows enabled streams queued before the output;

[0157]FIG. 70 shows a spatial decoder buffer;

[0158]FIG. 71 shows a buffer pointer;

[0159]FIG. 72 shows a video demux;

[0160]FIG. 73 shows a construction of a picture;

[0161]FIG. 74 shows a construction of a 4:2:2 macroblock;

[0162]FIG. 75 shows a calculating macroblock dimension from pel ones;

[0163]FIG. 76 shows spatial decoding;

[0164]FIG. 77 shows an overview of H.261 inverse quantization;

[0165]FIG. 78 shows an overview of JPEG inverse quantization;

[0166]FIG. 79 shows an overview of MPEG inverse quantization;

[0167]FIG. 80 shows a quantization table memory map;

[0168]FIG. 81 shows an overview of JPEG baseline sequential structure;

[0169]FIG. 82 shows a tokenised JPEG picture;

[0170]FIG. 83 shows a temporal decoder;

[0171]FIG. 84 shows a picture buffer specification;

[0172]FIG. 85 shows an MPEG picture sequence (m=3);

[0173]FIG. 86 shows how “I” pictures are stored and output;

[0174]FIG. 87 shows how “P” pictures are formed, stored and output;

[0175]FIG. 88 shows how “B” pictures are formed and output;

[0176]FIG. 89 shows P picture formation;

[0177]FIG. 90 shows H.261 prediction formation;

[0178]FIG. 91 shows an H.261 “sequence”;

[0179]FIG. 92 shows a hierarchy of H.261 syntax;

[0180]FIG. 93 shows an H.261 picture layer;

[0181]FIG. 94 shows an H.261 arrangement of groups of blocks;

[0182]FIG. 95 shows an H.261 “slice” layer;

[0183]FIG. 96 shows an H.261 arrangement of macroblocks;

[0184]FIG. 97 shows an H.261 sequence of blocks;

[0185]FIG. 98 shows an H.261 macroblock layer;

[0186]FIG. 99 shows an H.261 arrangement of pels in blocks;

[0187]FIG. 100 shows a hierarchy of MPEG syntax;

[0188]FIG. 101 shows an MPEG sequence layer;

[0189]FIG. 102 shows an MPEG group of pictures layer;

[0190]FIG. 103 shows an MPEG picture layer;

[0191]FIG. 104 shows an MPEG “slice” layer;

[0192]FIG. 105 shows an MPEG sequence of blocks;

[0193]FIG. 106 shows an MPEG macroblock layer;

[0194]FIG. 107 shows an “open GOP”;

[0195]FIG. 108 shows examples of access structure;

[0196]FIG. 109 shows access start timing;

[0197]FIG. 110 shows a fast page read cycle;

[0198]FIG. 111 shows a fast page write cycle;

[0199]FIG. 112 shows a refresh cycle;

[0200]FIG. 113 shows extracting row and column address from a chipaddress;

[0201]FIG. 114 shows timing parameters for any strobe signal;

[0202]FIG. 115 shows timing parameters between any two strobe signals;

[0203]FIG. 116 shows timing parameters between a bus and a strobe;

[0204]FIG. 117 shows timing parameters between a bus and a strobe;

[0205]FIG. 118 shows a Huffman decoder and parser;

[0206]FIG. 119 shows an H.261 and an MPEG AC Coefficient Decoding FlowChart;

[0207]FIG. 120 shows a block diagram for JPEG (AC and DC) coefficientdecoding;

[0208]FIG. 121 shows a flow diagram for JPEG (AC and DC) coefficientdecoding;

[0209]FIG. 122 shows an interface to the Huffman Token Formatter;

[0210]FIG. 123 shows a token formatter block diagram;

[0211]FIG. 124 shows an H.261 and an MPEG AC Coefficient Decoding;

[0212]FIG. 125 shows the interface to the Huffman ALU;

[0213]FIG. 126 shows the basic structure of the Huffman ALU;

[0214]FIG. 127 shows the buffer manager;

[0215]FIG. 128 shows an imodel and hsppk block diagram;

[0216]FIG. 129 shows an imex state diagram;

[0217]FIG. 130 illustrates the buffer start-up;

[0218]FIG. 131 shows a DRAM interface;

[0219]FIG. 132 shows a write swing buffer;

[0220]FIG. 133 shows an arithmetic block;

[0221]FIG. 134 shows an iq block diagram;

[0222]FIG. 135 shows an iqca state machine;

[0223]FIG. 136 shows an IDCT 1-D Transform Algorithm;

[0224]FIG. 137 shows an IDCT 1-D Transform Architecture;

[0225]FIG. 138 shows a token stream block diagram;

[0226]FIG. 139 shows a standard block structure;

[0227]FIG. 140 is a block diagram showing; microprocessor test access;

[0228]FIG. 141 shows 1-D Transform Micro-Architecture;

[0229]FIG. 142 shows a temporal decoder block diagram;

[0230]FIG. 143 shows the structure of at Two-wire interface stage;

[0231]FIG. 144 shows the address generator block diagram;

[0232]FIG. 145 shows the block and pixel offsets;

[0233]FIG. 146 shows multiple prediction filters;

[0234]FIG. 147 shows a single prediction filter;

[0235]FIG. 148 shows the 1-D prediction filter;

[0236]FIG. 149 shows a block of pixels;

[0237]FIG. 150 shows the structure of the read rudder;

[0238]FIG. 151 shows the block and pixel offsets;

[0239]FIG. 152 shows a prediction example;

[0240]FIG. 153 shows the read cycle;

[0241]FIG. 154 shows the write cycle;

[0242]FIG. 155 shows the top-level registers block diagram with timingreferences;

[0243]FIG. 156 shows the control for incrementing presentation numbers;

[0244]FIG. 157 shows the buffer manager state machine (complete);

[0245]FIG. 158 shows the state machine main loop;

[0246]FIG. 159 shows the buffer 0 containing an SIF (22 by 18macroblocks) picture;

[0247]FIG. 160 shows the SIF component 0 with a display window;

[0248]FIG. 161 shows an example picture format showing storage blockaddress;

[0249]FIG. 162 shows a buffer 0 containing a SIF (22 by 18 macroblocks)picture;

[0250]FIG. 163 shows an example address calculation;

[0251]FIG. 164 shows a write address generation state machine;

[0252]FIG. 165 shows a slice of the datapath;

[0253]FIG. 166 shows a two cycle operation of the datapath;

[0254]FIG. 167 shows mode 1 filtering;

[0255]FIG. 168 shows a horizontal up-sampler datapath; and

[0256]FIG. 169 shows the structure of the color-space converter.

[0257] In the ensuing description of the practice of the invention, thefollowing terms are frequently used and are generally defined by thefollowing glossary:

GLOSSARY

[0258] BLOCK: An 8-row by 8-column matrix of pels, or 64 DCTcoefficients (source, quantized or dequantized).

[0259] CHROMINANCE (COMPONENT): A matrix, block or single pelrepresenting one of the two color difference signals related to theprimary colors in the manner defined in the bit stream. The symbols usedfor the color difference signals are Cr and Cb.

[0260] CODED REPRESENTATION: A data element as represented in itsencoded form.

[0261] CODED VIDEO BIT STREAM: A coded representation of a series of oneor more pictures as defined in this specification.

[0262] CODED ORDER: The order in which the pictures are transmitted anddecoded. This order is not necessarily the same as the display order.

[0263] COMPONENT: A matrix, block or single pel from one of the threematrices (luminance and two chrominance) that make up a picture.

[0264] COMPRESSION: Reduction in the number of bits used to represent anitem of data.

[0265] DECODER: An embodiment of a decoding process.

[0266] DECODING (PROCESS): The process defined in this specificationthat reads an input coded bitstream and produces decoded pictures oraudio samples.

[0267] DISPLAY ORDER: The order in which the decoded pictures aredisplayed. Typically, this is the same order in which they werepresented at the input of the encoder.

[0268] ENCODING (PROCESS): A process, not specified in thisspecification, that reads a stream of input pictures or audio samplesand produces a valid coded bitstream as defined in this specification.

[0269] INTRA CODING: Coding of a macroblock or picture that usesinformation only from that macroblock or picture.

[0270] LUMINANCE (COMPONENT): A matrix, block or single pel representinga monochrome representation of the signal and related to the primarycolors in the-manner defined in the bit stream. The symbol used forluminance is Y.

[0271] MACROBLOCK: The four 8 by 8 blocks of luminance data and the two(for 4:2:0 chroma format) four (for 4:2:2 chroma format) or eight (for4:4:4 chroma format) corresponding 8 by 8 blocks of chrominance datacoming from a 16 by 16 section of the luminance component of thepicture. Macroblock is sometimes used to refer to the pel data andsometimes to the coded representation of the pel values and other dataelements defined in the macroblock header of the syntax defined in thispart of this specification. To one of ordinary skill in the art, theusage is clear from the context.

[0272] MOTION COMPENSATION: The use of motion vectors to improve theefficiency of the prediction of pel values. The prediction uses motionvectors to provide offsets into the past and/or future referencepictures containing previously decoded pel values that are used to formthe prediction error signal.

[0273] MOTION VECTOR: A two-dimensional vector used for motioncompensation that provides an offset from the coordinate position in thecurrent picture to the coordinates in a reference picture.

[0274] NON-INTRA CODING: Coding of a macroblock or picture that usesinformation both from itself and from macroblocks and pictures occurringat other times.

[0275] PEL. Picture element.

[0276] PICTURE: Source, coded or reconstructed image data. A source orreconstructed picture consists of three rectangular matrices of 8-bitnumbers representing the luminance and two chrominance signals. Forprogressive video, a picture is identical to a frame, while forinterlaced video, a picture can refer to a frame, or the top field orthe bottom field of the frame depending on the context.

[0277] PREDICTION: The use of a predictor to provide an estimate of thepel value or data element currently being decoded.

[0278] RECONFIGURABLE PROCESS STAGE (RPS): A stage, which in response toa recognized token, reconfigures itself to perform various operations.

[0279] SLICE: A series of macroblocks.

[0280] TOKEN: A universal adaptation unit in the form of an interactiveinterfacing messenger package for control and/or data functions.

[0281] START CODES [SYSTEM AND VIDEO]: 32-bit codes embedded in a codedbitstream that are unique. They are used for several purposes includingidentifying some of the structures in the coding syntax.

[0282] VARIABLE LENGTH CODING; VLC: A reversible procedure for codingthat assigns shorter code-words to frequent events and longer code-wordsto less frequent events.

[0283] VIDEO SEQUENCE: A series of one or more pictures.

[0284] Detailed Descriptions

DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

[0285] As an introduction to the most general features used in apipeline system which is utilized in the preferred embodiments of theinvention, FIG. 1 is a greatly simplified illustration of six cycles ofa six-stage pipeline. (As is explained in greater detail below, thepreferred embodiment of the pipeline includes several advantageousfeatures not shown in FIG. 1.).

[0286] Referring now to the drawings, wherein like reference numeralsdenote like or corresponding elements throughout the various figures ofthe drawings, and more particularly to FIG. 1, there is shown a blockdiagram of six cycles in practice of the present invention. Each row ofboxes illustrates a cycle and each of the different stages are labelledA-F, respectively. Each shaded box indicates that the correspondingstage holds valid data, i.e., data that is to be processed in one of thepipeline stages. After processing (which may involve nothing more than asimple transfer without manipulation of the data) valid data istransferred out of the pipeline as valid output data.

[0287] Note that an actual pipeline application may include more orfewer than six pipeline stages. As will be appreciated, the presentinvention may be used with any number of pipeline stages. Furthermore,data may be processed in more than one stage and the processing time fordifferent stages can differ.

[0288] In addition to clock and data signals (described below), thepipeline includes two transfer control signals—a “VALID” signal and an“ACCEPT” signal. These signals are used to control the transfer of datawithin the pipeline. The VALID signal, which is illustrated as the upperof the two lines connecting neighboring stages, is passed in a forwardor downstream direction from each pipeline stage to the nearestneighboring device. This device may be another pipeline stage or someother system. For example, the last pipeline stage may pass its data onto subsequent processing circuitry. The ACCEPT signal, which isillustrated as the lower of the two lines connecting neighboring stages,passes in the other direction upstream to a preceding device.

[0289] A data pipeline system of the type used in the practice of thepresent invention has, in preferred embodiments, one or more of thefollowing characteristics:

[0290] 1. The pipeline is “elastic” such that a delay at a particularpipeline stage causes the minimum disturbance possible to other pipelinestages. Succeeding pipeline stages are allowed to continue processingand, therefore, this means that gaps open up in the stream of datafollowing the delayed stage. Similarly, preceding pipeline stages mayalso continue where possible. In this case, any gaps in the data streammay, wherever possible, be removed from the stream of data.

[0291] 2. Control signals that arbitrate the pipeline are organized sothat they only propagate to the nearest neighboring pipeline stages. Inthe case of signals flowing in the same direction as the data flow, thisis the immediately succeeding stage. In the case of signals flowing inthe opposite direction to the data flow, this is the immediatelypreceding stage.

[0292] 3. The data in the pipeline is encoded such that many differenttypes of data are processed in the pipeline. This encoding accommodatesdata packets of variable size and the size of the packet need not beknown in advance.

[0293] 4. The overhead associated with describing the type of data is assmall as possible.

[0294] 5. It is possible for each pipeline stage to recognize only theminimum number of data types that are needed for its required function.It should, however, still be able to pass all data types onto thesucceeding stage even though it does not recognize them. This enablescommunication between non-adjacent pipeline stages.

[0295] Although not shown in FIG. 1, there are data lines, either singlelines or several parallel lines, which form a data bus that also leadinto and out of each pipeline stage. As is explained and illustrated ingreater detail below, data is transferred into, out of, and between thestages of the pipeline over the data lines.

[0296] Note that the first pipeline stage may receive data and controlsignals from any form of preceding device. For example, receptioncircuitry of a digital image transmission system, another pipeline, orthe like. On the other hand, it may generate itself, all or part of thedata to be processed in the pipeline. Indeed, as is explained below, a“stage” may contain arbitrary processing circuitry, including none atall (for simple passing of data) or entire systems (for example, anotherpipeline or even multiple systems or pipelines), and it may generate,change, and delete data as desired.

[0297] When a pipeline stage contains valid data that is to betransferred down the pipeline, the VALID signal, which indicates datavalidity, need not be transferred further than to the immediatelysubsequent pipeline stage. A two-wire interface is, therefore, includedbetween every pair of pipeline stages in the system. This includes atwo-wire interface between a preceding device and the first stage, andbetween a subsequent device and the last stage, if such other devicesare included and data is to be transferred between them and thepipeline.

[0298] Each of the signals, ACCEPT and VALID, has a HIGH and a lowvalue. These values are abbreviated as “H” and “L”, respectively. Themost common applications of the pipeline. in practicing the invention,will typically be digital. In such digital implementations, the HIGHvalue may, for example, be a logical “1” and the LOW value may be alogical “O”. The system is not restricted to digital implementations,however, and in analog implementations, the HIGH value may be a voltageor other similar quantity above (or below) a set threshold, with the LOWvalue being indicated by the corresponding signal being below (or above)the same or some other threshold. For digital applications, the presentinvention may be implemented using any known technology, such as CMOS,bipolar etc.

[0299] It is not necessary to use a distinct storage device and wires toprovide for storage of VALID signals. This is true even in a digitalembodiment. All that is required is that the indication of “validity” ofthe data be stored along with the data. By way of example only, indigital television pictures that are represented by digital values, asspecified in the international standard CCIR 601, certain specificvalues are not allowed. In this system, eight-bit binary numbers areused to represent samples of the picture and the values zero and 255 maynot be used.

[0300] If such a picture were to be processed in a pipeline built in thepractice of the present invention, then one of these values (zero, forexample) could be used to indicate that the data in a specific stage inthe pipeline is not valid. Accordingly, any non-zero data would bedeemed to be valid. In this example, there is no specific latch that canbe identified and said to be storing the “validness” of the associateddata. Nonetheless, the validity of the data is stored along with thedata.

[0301] As shown in FIG. 1, the state of the VALID signal into each stageis indicated as an “HH” or an “L” on an upper, right-pointed arrow.Therefore, the VALID signal from Stage into Stage B is LOW, and theVALID signal from Stage D into Stage E is HIGH. The state of the ACCEPTsignal into each stage is indicated as an “HI or an “L” on a lower,left-pointing arrow. Hence, the ACCEPT signal from Stage E into Stage Dis HIGH, whereas the ACCEPT signal from the device connected downstreamof the pipeline into Stage F is LOW.

[0302] Data is transferred from one stage to another during a cycle(explained below) whenever the ACCEPT signal of the downstream stageinto its upstream neighbor is HIGH. If the ACCEPT signal is LOW betweentwo stages, then data is not transferred between these stages.

[0303] Referring again to FIG. 1, if a box is shaded, the nocorresponding pipeline stage is assumed, by way of example, to containvalid output data. Likewise, the VALID signal which is passed from thatstage to the following stage is HIGH. FIG. 1 illustrates the pipelinewhen stages B, D, and E contain valid data. Stages A, C, and F do notcontain valid data. At the beginning, the VALID signal into pipelinestage A is HIGH, meaning that the data on the transmission line into thepipeline is valid.

[0304] Also at this time, the ACCEPT signal into pipeline stage F isLOW, so that no data, whether valid or not, is transferred out of StageF. Note that both valid and invalid data is transferred between pipelinestages. Invalid data, which is data not worth saving, may be writtenover, thereby, eliminating it from the pipeline. However, valid datamust not be written over since it is data that must be saved forprocessing or use in a downstream device e.g., a pipeline stage, adevice or a system connected to the pipeline that receives data from thepipeline.

[0305] In the pipeline illustrated in FIG. 1, Stage E contains validdata D1, Stage D contains valid data D2, Stage B contains valid data D3,and a device (not shown) connected t the pipeline upstream contains dataD4 that is to be transferred into and processed in the pipeline. StagesB, D and E, in addition to the upstream device, contain valid data and,therefore, the VALID signal from these stages or devices into theirrespective following devices is HIGH. The VALID signal from the StagesA, C and F is, however, LOW since these stages do not contain validdata.

[0306] Assume now that the device connected downstream from the pipelineis not ready to accept data from the pipeline. The device signals thisby setting the corresponding ACCEPT signal LOW into Stage F. Stage Fitself, however, does not contain valid data and is, therefore, able toaccept data from the preceding Stage E. Hence, the ACCEPT signal fromStage F into Stage E is set HIGH.

[0307] Similarly, Stage E contains valid data and Stage F is ready toaccept this data. Hence, Stage E can accept new data as long as thevalid data D1 is first transferred to Stage F. In other words, althoughStage F cannot transfer data downstream, all the other stages can do sowithout any valid data being overwritten or lost. At the end of Cycle 1,data can, therefore, be “shifted” one step to the right. This conditionis shown in Cycle 2.

[0308] In the illustrated example, the downstream device is still notready to accept new data in Cycle 2 and, therefore, the ACCEPT signalinto Stage F is still LOW. Stage F cannot, therefore, accept new datasince doing so would cause valid data D1 to be overwritten and lost. TheACCEPT signal from Stage F into Stage E, therefore, goes LOW, as doesthe ACCEPT signal from Stage E into Stage D since Stage E also containsvalid data D2. All of the Stages A-D, however, are able to accept newdata (either because they do not contain valid data or because they areable to shift their valid data downstream and accept near data) and theysignal this condition to their immediately preceding neighbors bysetting their corresponding ACCEPT signals HIGH.

[0309] The state of the pipelines after Cycle 2 is illustrated in FIG. 1for the row labelled Cycle 3. By way of example, it is assumed that thedownstream device is still not ready to accept new data from Stage F(the ACCEPT signal into Stage F is LOW). Stages E and F, therefore, arestill “blocked”, but in Cycle 3, Stage D has received the valid data D3,which has overwritten the invalid data that was previously in thisstage. Since Stage D cannot pass on data D3 in Cycle 3, it cannot acceptnew data and, therefore, sets the ACCEPT signal into Stage C LOW.However, stages A-C are ready to accept new data and signal this bysetting their corresponding ACCEPT signals HIGH. Note that data D4 hasbeen shifted from Stage A to Stage B.

[0310] Assume now that the downstream device becomes ready to accept newdata in Cycle 4. It signals this to the pipeline by setting the ACCEPTsignal into Stage F HIGH. Although Stages C-F contain valid data, theycan now shift the data downstream and are, thus, able to accept newdata. Since each stage is therefore able to shift data one stepdownstream, they set their respective ACCEPT signals out HIGH.

[0311] As long as the ACCEPT signal into the final pipeline stage (inthis example, Stage F) is HIGH, the pipeline shown in FIG. 1 acts as arigid pipeline and simply shifts data one step downstream on each cycle.Accordingly, in Cycle 5, data D1, which was contained in Stage F inCycle 4, is shifted out of the pipeline to the subsequent device, andall other data is shifted one step downstream.

[0312] Assume now, that the ACCEPT signal into Stage F goes LOW in Cycle5. Once again, this means that Stages D-F are not able to accept newdata, and the ACCEPT signals out of these stages into their immediatelypreceding neighbors go LOW.

[0313] Hence, the data D2, D3 and D4 cannot shift downstream, however,the data D5 can. The corresponding state of the pipeline after Cycle 5is, thus, shown in FIG. 1 as Cycle 6.

[0314] The ability of the pipeline, in accordance with the preferredembodiments of the present invention, to “fill up” empty processingstages is highly advantageous since the processing stages in thepipeline thereby become decouple from one another. In other words, eventhough a pipeline stage may not be ready to accept data, the entirepipeline 5 does not have to stop and wait for the delayed stage. Rather,when one stage is unable to accept valid data it simply forms atemporary “wall” in the pipeline. Nonetheless, stages downstream of the“wall” can continue to advance valid data even to circuitry connected tothe pipeline, and stages to the left of the “wall” can still accept andtransfer valid data downstream. Even when several pipeline stagestemporarily cannot accept new data, other stages can continue to operatenormally. In particular, the pipeline can continue to accept data intoits initial stage A as long as stage A does not already contain validdata that cannot be advanced due to the next stage not being ready toaccept new data. As this example illustrates, data can be transferredinto the pipeline and between stages even when one or more processingstages is blocked.

[0315] In the embodiment shown in FIG. 1, it is assumed that the variouspipeline stages do not store the ACCEPT signals they receive from theirimmediately following neighbors. Instead, whenever the ACCEPT signalinto a downstream stage goes LOW, this LOW signal is propagated upstreamas far as the nearest pipeline stage that does not contain valid data.For example, referring to FIG. 1, it was assumed that the ACCEPT signalinto Stage F goes LOW in Cycle 1. In Cycle 2, the LOW signal propagatesfrom Stage F back to Stage D.

[0316] In Cycle 3, when the data D3 is latched into Stage D, the ACCEPTsignal propagates upstream four stages to Stage C. When he ACCEPT signalinto Stage F goes HIGH in Cycle 4, it must propagate upstream all theway to Stage C. In other words, the change in the ACCEPT signal mustpropagate back four stages. It is not necessary, however, in theembodiment illustrated in FIG. 1, for the ACCEPT signal to propagate allthe way back to the beginning of the pipeline if there is someintermediate stage that is able to accept new data.

[0317] In the embodiment illustrated in FIG. 1, each pipeline stage willstill need separate input and output data latches to allow data to betransferred between stages without unintended overwriting. Also,although the pipeline illustrated in FIG. 1 is able to “compress” whendownstream pipeline stages are blocked, i.e., they cannot pass on thedata they contain, the pipeline does not “expand” to provide stages thatcontain no valid data between stages that do contain valid data. Rather,the ability to compress depends on there being cycles during which novalid data is presented to the first pipeline stage.

[0318] In Cycle 4, for example, if the ACCEPT signal into Stage Fremained LOW and valid data filled pipeline stages A and B, as long asvalid data continued to be presented to Stage A the pipeline would notbe able to compress any further and valid input data could be lost.Nonetheless, the pipeline illustrated in FIG. 1 reduces the risk of dataloss since it is able to compress as long as there is a pipeline stagethat does not contain valid data.

[0319]FIG. 2 illustrates another embodiment of the pipeline that canboth compress and expand in a logical manner and which includescircuitry that limits propagation of the ACCEPT signal to the nearestpreceding stage. Although the circuitry for implementing this embodimentis explained and illustrated in greater detail below, FIG. 2 serves toillustrate the principle by which it operates.

[0320] For ease of comparison only, the input data and ACCEPT spiralsinto the pipeline embodiment shown in FIG. 2 are the sane as in thepipeline embodiment shown in FIG. 1. Accordingly, stages E, D and Bcontain valid data D1, D2 and C3, respectively. The ACCEPT signal intoStage F is LOW; and data D4 is presented to the beginning pipeline StageA. In FIG. 2, three lines are shown connecting each neighboring pair ofpipeline stages. The uppermost line, which may be a bus, is a data line.The middle line is the line over which the VALID signal is transferred,while the bottom line is the line over which the ACCEPT signal istransferred. Also, as before, the ACCEPT signal into Stage F remains LOWexcept in Cycle 4. Furthermore, additional data D5 is presented to thepipeline in Cycle 4.

[0321] In FIG. 2, each pipeline stage is represented as a block dividedinto two halves to illustrate that each stage in this embodiment of thepipeline includes primary and secondary data storage elements. In FIG.2, the primary data storage is shown as the right half of each stage.However, it will be appreciated that this delineation is for the purposeof illustration only and is not intended as a limitation.

[0322] As FIG. 2 illustrates, as long as the ACCEPT signal into a stageis HIGH, data is transferred from the primary storage elements of thestage to the secondary storage elements of the following stage duringany given cycle. Accordingly, although the ACCEPT signal into Stage F isLOW, the ACCEPT signal into all other stages is HIGH so that the dataD1, D2 and D3 is shifted forward one stage in Cycle 2 and the data D4 isshifted into the first Stage A.

[0323] Up to this point, the pipeline embodiment shown in FIG. 2 acts ina manner similar to the pipeline embodiment shown in FIG. 1. The ACCEPTsignal from Stage F into Stage E, however, is HIGH even though theACCEPT signal into Stage F is LOW. As is explained below, because of thesecondary storage elements, it is not necessary for the LOW ACCEPTsignal to propagate upstream beyond Stage F. Moreover, by leaving theACCEPT signal into Stage E HIGH, Stage F signals that it is ready toaccept new data. Since Stage F is not able transfer the data D1 in itsprimary storage elements downstream (the ACCEPT signal into Stage F isLOW) in Cycle 3, Stage E must, therefore, transfer the data D2 into thesecondary storage elements of Stage F. Since both the primary and thesecondary storage elements of Stage F now contain valid data that cannotbe passed on, the ACCEPT signal from Stage F into Stage E is set LOW.Accordingly, this represents a propagation of the LOW ACCEPT signal backonly one stage relative to Cycle 2, whereas this ACCEPT signal had to bepropagated back all the way to Stage C in the embodiment shown in FIG.1.

[0324] Since Stages A-E are able to pass on their data, the ACCEPTsignals from the stages into their immediately preceding neighbors areset HIGH. Consequently, the data D3 and D4 are shifted one stage to theright so that, in Cycle 4, they are loaded into the primary data storageelements of Stage E and Stage C, respectively. Although Stage E nowcontains valid data D3 in its primary storage elements, its secondarystorage elements can still be used to store other data without risk ofover-writing any valid data.

[0325] Assume now, as before, that the ACCEPT signal into Stage Fbecomes HIGH in Cycle 4. This indicates that the downstream device towhich the pipeline passes data is ready to accept data from thepipeline. Stage F, however, has set its ACCEPT signal LOW and, thus,indicates to Stage E that Stage F is not prepared to accept new data.Observe that the ACCEPT signals for each cycle indicate what will“happen” in the next cycle, that is, whether data will be passed on(ACCEPT HIGH) or whether data must remain in place (ACCEPT LOW)).Therefore, from Cycle 4 to Cycle 5, the data D1 is passed from Stage Fto the following device, the data D2 is shifted from secondary toprimary storage in Stage F, but the data C3 in Stage E is nottransferred to Stage F. The data D4 and D: can be transferred into thefollowing pipeline stages as normal since the following stages havetheir ACCEPT signals HIGH.

[0326] Comparing the state of the pipeline in Cycle 4 and Cycle 5, itcan be seen that the provision of secondary storage elements, enablesthe pipeline embodiment shown in FIG. 2 to expand, that is, to free updata storage elements into which valid data can be advanced. Forexample, in Cycle 4, the data blocks D1, D2 and D3 form a “solid wall”since their data cannot be transferred until the ACCEPT signal intoStage F goes HIGH. Once this signal does become HIGH, however, data D1is shifted out of the pipeline, data D2 is shifted into the primarystorage elements of Stage F, and the secondary storage elements of StageF become free to accept new data if the following device is not able toreceive the data D2 and the pipeline must once again “compress.” This isis shown in Cycle 6, for which the data D3 has been shifted into thesecondary storage elements of Stage F and the data D4 has been passed onfrom Stage D to Stage E as normal. FIGS. 3a(1), 3 a(2), 3 b(1) and 3b(2) (which are referred to collectively as FIG. 3) illustrate generallya preferred embodiment of the pipeline. This preferred embodimentimplements the structure shown in FIG. 2 using a two-phase,non-overlapping clock with phases o0 and o1. Although a two-phase clockis preferred, it will be appreciated that it is also possible to drivethe various embodiments of the invention using a clock with more thantwo phases.

[0327] As shown in FIG. 3, each pipeline stage is represented as havingtwo separate boxes which illustrate the primary and secondary storageelements. Also, although the VALID signal and the data lines connect thevarious pipeline stages as before, for ease of illustration, only theACCEPT signal is shown in FIG. 3. A change of state during a clock phaseof certain of the ACCEPT signals is indicated in FIG. 3 using anupward-pointing arrow for changes from LOW to HIGH Similarly, adownward-pointing arrow for changes from HIGH to LOW. Transfer of datafrom one storage element to another is indicated by a large open arrow.It is assumed that the SQUALID signal out of the primary or secondarystorage elements of any given stage is HIGH whenever the storageelements contain valid data.

[0328] In FIG. 3, each cycle is shown as consisting of a full period ofthe non-overlapping clock phases o0 and o1. As is explained in greaterdetail below, data is transferred from the secondary storage elements(shown as the left box in each stage) to the primary storage elements(shown as the right box in each stage) during clock cycle o1, whereasdata is transferred from the primary storage elements of one stage tothe secondary storage elements of the following stage during the clockcycle o0. FIG. 3 also illustrates that the primary and secondary storageelements in each stage are further connected via an internal acceptanceline to pass an ACCEPT signal in the same manner that the ACCEPT signalis passed from stage to stage. In this way, the secondary storageelement will know when it can pass its date to the primary storageelement.

[0329]FIG. 3 shows the o1 phase of Cycle 1, in which data D1, D2 and D3,which were previously shifted into the secondary storage elements ofStages E, D and B, respectively, are shifted into the primary storageelements of the respective stage. During the o1 phase of Cycle 1, thepipeline, therefore, assumes the same configuration as is shown as Cycle1 of FIG. 2. As before, the ACCEPT signal into Stage F is assumed to beLOW. As FIG. 3 illustrates, however, this means that the ACCEPT signalinto the primary storage element of Stage F is LOW, but since thisstorage element does not contain valid data, it sets the ACCEPT signalinto its secondary storage element HIGH.

[0330] The ACCEPT signal from the secondary storage elements of Stage Finto the primary storage elements of Stage E is also set HIGH since thesecondary storage elements of Stage F do not contain valid data. Asbefore, since the primary storage elements of Stage F are able to acceptdata, data in all the upstream primary and secondary storage elementscan be shifted downstream without any valid data being overwritten. Theshift of data from one stage to the next takes place during the next o0phase in Cycle 2. For example, the valid data D1 contained in theprimary storage element of Stage E is shifted into the secondary storageelement of Stage F, the data D4 is shifted into the pipeline, that is,into the secondary storage element of Stage A, and so forth.

[0331] The primary storage element of Stage F still does not containvalid data during the o0 phase in Cycle 2 and, therefore, the ACCEPTsignal from the primary storage elements into the secondary storageelements of Stage F remains HIGH. During the o1 phase in Cycle 2, datacan therefore be shifted yet another step to the right, i.e., from thesecondary to the primary storage elements within each stage.

[0332] However, once valid data is loaded into the primary storageelements of Stage F, if the ACCEPT into Stage F from the downstreamdevice is still LOW, it is not possible to shift data out of thesecondary storage element of Stage F without overwriting and destroyingthe valid data D1. The ACCEPT signal from the primary storage elementsinto he secondary storage elements of Stage F therefore goes LOW. DataD2, however, can still be shifted into the secondary storage of Stage Fsince it did not contain valid data and its ACCEPT signal out was HIGH.

[0333] During the o1 phase of Cycle 3, it is not possible to shift dataD2 into the primary storage elements of Stage F although data can beshifted within all the previous stages. Once valid data is loaded intothe secondary storage elements of Stage F, however, Stage F is not ableto pass on this data. It signals this event setting its ACCEPT signalout LOw.

[0334] Assuming that the ACCEPT signal into Stage F remains LOW, dataupstream of Stage F can continue to be shifted between stages and withinstages on the respective clock phases until the next valid data block D3reaches the primary storage elements of Stage E. As illustrated, thiscondition is reached during the o1 phase of Cycle 4.

[0335] During the o0 phase of Cycle 5, data D3 has been loaded into theprimary storage element of Stage E. Since this data cannot be shiftedfurther, the ACCEPT signal out of the primary storage elements of StageE is set LOW. Upstream data can be shifted as normal.

[0336] Assume now, as in Cycle 5 of FIG. 2, that the device connecteddownstream of the pipeline is able to accept pipeline data. It signalsthis event by setting the ACCEPT signal into pipeline Stage F HIGHduring the o1 phase of Cycle 4. The primary storage elements of Stage Fcan now shift data to the right and they are also able to accept newdata. Hence, the data D1 was shifted out during the o1 phase of Cycle 5so that the primary storage elements of Stage F no longer contain datathat must be saved. During the o1 phase of Cycle 5, the data D2 is,therefore, shifted within Stage F from the secondary storage elements tothe primary storage elements. The secondary storage elements of Stage Fare also able to accept new data and signal this by setting the ACCEPTsignal into the primary storage elements of Stage E HIGH. Duringtransfer of data within a stage, that is, from its secondary to itsprimary storage elements, both sets of storage elements will contain thesame data, but the data in the secondary storage elements can beoverwritten with no data loss since this data will also be held in theprimary storage elements. The same holds true for data transfer from theprimary storage elements of one stage into the secondary storageelements of a subsequent stage.

[0337] Assume now, that the ACCEPT signal into the primary storageelements of Stage F goes LOW during the o1 phase in Cycle 5. This meansthat Stage F is not able to transfer the data D2 out of the pipeline.Stage F, consequently, sets the ACCEPT signal from its primary to itssecondary storage elements LOW to prevent overwriting of the valid dataD2. The data D2 stored in the secondary storage elements of Stage F,however, can be overwritten without loss, and the data D3, is therefore,transferred into the secondary storage elements of Stage F during the o0phase of Cycle 6. Data D4 and D5 can be shifted downstream as normal.Once valid data D3 is stored in Stage F along with data D2, as long asthe ACCEPT signal into the primary storage elements of Stage F is LOW,neither of the secondary storage elements can accept new data, and itsignals this by setting the ACCEPT signal into Stage E LOW.

[0338] When the ACCEPT signal into the pipeline from the downstreamdevice changes from LOW to HIGH or vice versa, this change does not haveto propagate upstream within the pipeline further than to theimmediately preceding storage elements (within the same stage or withinthe preceding pipeline stage). Rather, this change propagates upstreamwithin the pipeline one storage element block per clock phase.

[0339] As this example illustrates, the concept of a “stage” in thepipeline structure illustrated in FIG. 3 is to some extent a matter ofperception. Since data is transferred within a stage (from the secondaryto the primary storage elements) as it is between stages (from theprimary storage elements of the upstream stage into the secondarystorage elements of the neighboring downstream stage), one could us: aswell consider a stage to consist of “primary” storage elements followedby “secondary storage elements” instead of as illustrated in FIG. 3. Theconcept of “primary” and “secondary” storage elements is, therefore,mostly a question of labeling. In FIG. 3, the “primary” storage elementscan also be referred to as “output” storage elements, since they are theelements from which data is transferred out of a stage into a followingstage or device, and the “secondary” storage elements could be “input”storage elements for the same stage.

[0340] In explaining the aforementioned embodiments, as shown in FIGS.1-3, only the transfer of data under the control of the ACCEPT and VALIDsignals has been mentioned. It is to be further understood that eachpipeline stage may also process the data it has received arbitrarilybefore passing it between its internal storage elements or beforepassing it to the following pipeline stage. Therefore, referring onceagain to FIG. 3, a pipeline stage can, therefore, be defined as theportion of the pipeline that contains input and output storage elementsand that arbitrarily processes data stored in its storage elements.

[0341] Furthermore, the “device” downstream from the pipeline Stage F,need not be some other type of hardware structure, but rather it can beanother section of the same or part of another pipeline. As illustratedbelow, a pipeline stage can set its ACCEPT signal LOW not only when allof the downstream storage elements are filled with valid data, but alsowhen a stage requires more than one clock phase to finish processing itsdata. This also can occur when it creates valid data in one or both ofits storage elements. In other words, it is not necessary for a stagesimply to pass on the ACCEPT signal based on whether or not theimmediately downstream storage elements contains valid data that cannotbe passed on. Rather, the ACCEPT signal itself may also be alteredwithin the stage or, by circuitry external to the stage, in ordercontrol the passage of data between adjacent storage elements. The VALIDsignal may also be processed in an analogous manner.

[0342] A great advantage of the two-wire interface,(one wire for each ofthe VALID and ACCEPT signals) is its ability to D control the pipelinewithout the control signals needing to propagate back up the pipelineall the way to its beginning stage. Referring once again to FIG. 1,Cycle 3, for example, although stage F “tells” stage E that it cannotaccept data, and stage E tells stage D, and stage D tells stage C.Indeed, if there had been more stages containing valid data, then thissignal would have propagated back even further along the pipeline. Inthe embodiment shown in FIG. 3, Cycle 3, the LOW ACCEPT signal is notpropagated any further upstream than to Stage E and, then, only to itsprimary 1, storage elements.

[0343] As described below, this embodiment is able to achieve thisflexibility without adding significantly to the silicon area that isrequired to implement the design. Typically, each latch in the pipelineused for data storage requires only a single extra transistor (whichlays out very efficiently in silicon). In addition, two extra latchesand a small number of gates are preferably added to process the ACCEPTand VALID signals that are associated with the data latches in eachhalf-stage.

[0344]FIG. 4 illustrates a hardware structure that implements a stage asshown in FIG. 3.

[0345] By way of example only, it is assumed that eight-bit data is tobe transferred (with or without further Manipulation in optionalcombinatorial logic circuits) in parallel through the pipeline. However,it will be appreciated that either ore or less than eight-bit data canbe used in practicing the invention. Furthermore, the two-wire interfacein accordance with this embodiment is, however, suitable for use withany data bus width, and the data bus width may ever change from onestage to the next if a particular application so requires. The interfacein accordance with this embodiment can also be used to process analogsignals.

[0346] As discussed previously, while other conventional timingarrangements may be used, the interface is preferably controlled by atwo-phase, non-overlapping clock. In FIGS. 4-9, these clock phasesignals are referred to as PH0 and PH1. In FIG. 4, a line is shown foreach clock phase signal.

[0347] Input data enters a pipeline stage over a multi-bit data busIN_DATA and is transferred to a following pipeline stage or tosubsequent receiving circuitry over an output data bus OUT_DATA. Theinput data is first loaded in a manner described below into a series ofinput latches (one for each input data signal) collectively referred toas LDIN, which constitute the secondary storage elements describedabove.

[0348] In the illustrated example of this embodiment, it is assumed thatthe Q outputs of all latches follow their D inputs, that is, they are“loaded”, when the clock input is HIGH, i.e., at a logic “1” level.Additionally, the Q outputs hold their last values. In other words, theQ outputs are “latched” on the falling edge of their respective clocksignals. Each latch has for its clock either one of two non-overlappingclock signals PH0 or PH1 (as shown in FIG. 5), or the logical ANDcombination of one of these clock signals PH0, PH1 and one logic signal.The invention works equally well, however, by providing latches thatlatch on he rising edges of the clock signals, or any other knownlatching arrangement, as long as conventional methods are applied toensure proper timing of the latching operations.

[0349] The output data from the input data latch LDIN passes via anarbitrary and optional combinatorial logic circuit B1, which may beprovided to convert output data from input later. LDIN into intermediatedata, which is then later loaded in an output data latch LDOUT, whichcomprises the primary storage elements described above. The output fromthe output data latch LDOUT may similarly pass through an arbitrary andoptional combinatorial logic circuit B2 before being passed onward asOUTDATA to the next device downstream. This may be another pipelinestage or any other device connected to the pipeline.

[0350] In the practice of the present invention, each stage of thepipeline also includes a validation input latch LVIN, a validationoutput latch LVOUT, an acceptance input latch LAIN, and an acceptanceoutput latch LAOUT. Each of these four latches is, preferably, a simple,single-stage latch. The outputs from latches LVIN, LVOUT, LAIN and LAOUTare, respectively, QVIN, QVOUT, QAIN, QAOUT. The output signal QVIN fromthe validation input latch is connected either directly as an input tothe validation output latch LVOUT, or via intermediate logic devices orcircuits that may alter the signal.

[0351] Similarly, the output validation signal QVOUT of a given stagemay be connected either directly to the input of the validation inputlatch QVIN of the following stage, or via intermediate devices or logiccircuits, which may alter the validation signal. This output QVIN isalso connected to a logic gate (to be described below), whose output isconnected to the input of the acceptance input latch LAIN. The outputQAOUT from the acceptance output latch LAOUT is connected to a similarlogic gate (described below), optionally via another logic gate.

[0352] As shown in FIG. 4, the output validation signal QVOUT forms anOUT_VALID signa that can be received by subsequent stages as an IN_VALIDsignal, or simply to indicate valid data to subsequent circuityconnected to the pipeline. The readiness of the following circuit orstage to accept data is indicated to each stage as the signalOUT_ACCEPT, which is connected as the input to the acceptance outputlatch LAOUT, preferably via logic circuitry, which is described below.Similarly, the output QAOUT of the acceptance output latch LAOUT isconnected as the input to the acceptance input latch LAIN, preferablyvia logic circuitry, which is described below.

[0353] In practicing the present invention, the output signals QVIN,QVOUT from the validation latches LVIN, LVOUT are combined with theacceptance signals QAOUT, OUT ACCEPT, respectively, to form the inputsto the acceptance latches LAIN, LAOUT, respectively. In the embodimentillustrated in FIG. 4, these input signals are formed as the logicalNAND combination of the respective validation signals QVIN, QVOUT, withthe logical inverse of the respective acceptance output signals QAOUT,OUT_ACCEPT. Conventional logic gates, NAND1 and NAND2, perform the NANDoperation, and the inverters INV1, INV2 form the logical inverses of therespective acceptance signals.

[0354] As is well known in the art of digital design, the output from aNAND gate is a logical “1” when any or all of its input signals are inthe logical “0” state. The output from a NAND0 gate is, therefore, alogical “0” only when all of its inputs are in the logical “1” state.Also well known in the art, is that the output of a digital invertersuch as INV1 is a logical “1” when its input signal is a “0” and is a“0” when its input signal is a “1”.

[0355] The inputs to the NAND gate NAND1 are, therefore, QVIN and NOT(QAOUT), where “NOT” indicates binary inversion. Using known techniques,the input to the acceptance latch LAIN can be resolved as follows:

NAND(QVIN,NOT(QAOUT))=NOT(QVIN) OR QAOUT

[0356] In other words, the combination of the inverter INV1 and the NANDgate NAND1 is a logical “1” either when the signal QVIN is a “1” or thesignal QAOUT is a “1”, or both. The gate NAND1 and the inverter INV1can, therefore, be implemented by a single OR gate that has one of itsinputs tied directly to the QAOUT output of the acceptance latch LAOUTand its other input tied to the inverse of the output signal QVIN of thevalidation input latch LVIN.

[0357] As is well known in the art of digital design, many latchessuitable for use as the validation and acceptance latches may have twooutputs, Q and NOT(Q), that is, Q and its logical inverse. If suchlatches are chosen, the one input to the OR gate can, therefore, be tieddirectly to the NOT(Q) output of the validation latch LVIN. The gateNAND1 and the inverter INVL can be implemented using well knownconventional techniques. Depending on the latch architecture used,however, it may be more efficient to use a latch without an invertingoutput, and to provide instead the gate NANDI and the inverter INV1,both of which also can be implemented efficiently in a silicon device.Accordingly, any known arrangement may be used to generate the Q signaland/or its logical inverse.

[0358] The data and validation latches LDIN, LDOUT, LVIN and LVOUT, loadtheir respective data inputs when both clock signals (PH0 at the inputside and PH1 at the output side) and the output from the acceptancelatch of the same side are logical “1”. Thus, the clock signal (PH0 forthe input latches LDIN and LVIN) and the output of the respectiveacceptance latch (in this case, LAIN) are used in a logical AND mannerand data is loaded only when they are both logical “1”.

[0359] In particular applications, such as CMOS implementations of thelatches, the logical AND operation that controls the loading (via theillustrated CK or enabling “input”) of the latches can be implementedeasily in a conventional manner by connecting the respective enablinginput signals (for example, PH0 and QAIN for the latches LVIN and LDIN),to the gates of MOS transistors connected in series in the input linesof the latches. Consequently, is necessary to provide an actual logicAND gate, which might cause problems of timing due to propagation delayin high-speed applications.

[0360] The AND gate shown in the figures, therefore, only indicates thelogical function to be performed in generating the enable signals of thevarious latches.

[0361] Thus, the data latch LDIN loads input data only when PH0 and QAINare both “1”. It will latch this data when either of these two signalsgoes to a “0”.

[0362] Although only one of the clock phase signals PH0 or PH1, is usedto clock the data and validation latches at the input (and output) sideof the pipeline stage, the other clock phase signal is used, directly,to clock the acceptance latch at the same side. In other words, theacceptance latch on is either side (input or output) of a pipeline stageis preferably clocked “out of phase” with the data and validationlatches on the same side. For example, PH1 is used to clock theacceptance input latch, although PH0 is used in generating the clocksignal CK for the data latch LDIN and the validation latch LVIN.

[0363] As an example of the operation of a pipeline augmented by thetwo-wire validation and acceptance circuitry assume that no valid datais initially presented at the input to the circuit, either from apreceding pipeline stage, or from a transmission device. In other words,assume that the validation input signal IN_VALID to the illustratedstage has not gone to a “1” since the system was most recently reset.Assume further that several clock cycles have taken place since thesystem was last reset and, accordingly, the circuitry has reached asteady-state condition. The validation input signal QVIN from thevalidation latch LIVN is, therefore, loaded as a “0” during the nextpositive period of the clock PH0. The input to the acceptance inputlatch LAIN (via the gate NAND1 or another equivalent gate;, is,therefore, loaded as a “1” during the next positive period of the clocksignal PH1. In other words, since the data in the data input latch LDINis not valid, the stage signals that it is ready to accept input data(since it does not hold any data worth saving).

[0364] In this example, note that the signal IN_ACCEPT is used to enablethe data and validation latches LDIN and LVIN. Since the signalIN_ACCEPT at this time is a “1”, these latches effectively work asconventional transparent latches so that whatever data is on the IN_DATAbus simply is loaded into the data latch LDIN as soon as the clocksignal PH0 goes to a “1”. Of course, this invalid data will also beloaded into the next data latch LDOUT of the following pipeline stage aslong as the output QAOUT from its acceptance latch is a “11”.

[0365] Hence, as long as a data latch does not contain valid data, itaccepts or “loads” any data presented to it during the next positiveperiod of its respective clock signal. On the other hand, such invaliddata is not loaded in any stage or Which the acceptance signal from itscorresponding acceptance latch is low (that is, a “0”). Furthermore, theoutput signal from a validation latch (which forms the validation inputsignal to the subsequent validation latch) remains a “0” as long as thecorresponding IN_VALID (or QVIN) signal to the validation latch is low.

[0366] When the input data to a data latch is valid, the validationsignal IN_VALID indicates this by rising to a “1”. The output of thecorresponding validation latch then rises to a “1” on the next risingedge of its respective clock phase signal. For example, the validationinput signal QVIN of latch LVIN rises to a “1” when its correspondingIN_VALID signal goes high (that is, rises to a “1”) on the next risingedge of the clock phase signal PH0.

[0367] Assume now, instead, that the data input latch LDIN containsvalid data. If the data output latch LDOUT is read to accept new data,its acceptance signal QAOUT will be a “1”. In this case, during the nextpositive period of the clock signal PH1, the data latch LDOUT andvalidation latch LVOUT will be enabled, and the data latch LDOUT willload the data present at its input. This will occur before the nextrising edge of the other clock signal PH0, since the clock signals arenon-overlapping. At the next rising edge of PH0, the preceding datalatch (LDIN) will, therefore, not latch in new input data from thepreceding stage until the data output latch LDOUT has safely latched thedata transferred from the latch LDIN.

[0368] Accordingly, the same sequence is followed by every adjacent pairof data latches (within a stage or between adjacent stages) that areable to accept data, since they will be operating based on alternatephases of the clock. Any data latch that is not ready to accept new databecause it contains valid data that cannot yet be passed, will have anoutput acceptance signal (the QA output from its acceptance latch LA)that is LOW, and its data latch LDIN or LDCUT will not be loaded. Hence,as long as the acceptance signal (the output from the acceptance latch)of a given stage or side (input or output) of a stage is LOW, itscorresponding data latch will not be loaded.

[0369]FIG. 4 also shows a reset feature included in a preferredembodiment. In the illustrated example, a reset signal NOTRESETO isconnected to an inverting reset input R (inversion is hereby indicatedby a small circle, as is conventional) of the validation output latchLVOUT. As is well known, this means that the validation latch LVOUT willbe forced to output a “0” whenever the reset signal NOTREST0 becomes a“0”. One advantage of resetting the latch when the reset signal goes low(becomes a “0”) is that a break in transmission will reset the latches.They will then be in their “null” or reset state whenever a validtransmission begins and the reset signal goes HIGH. The reset signalNOTRESET0, therefore, operates as a digital “ON/OFF” switch, such thatit must be at a HIGH value in order to activate the pipeline.

[0370] Note that it is not necessary to reset all of the latches thathold valid data in the pipeline. As depicted in FIG. 4, the validationinput latch LVIN is not directly reset by the reset signal NOTRESETO,but rather is reset indirectly. Assume that the reset signal NOTRESETOdrops to a “0”. The validation output signal QVOUT also drops to a “0”,regardless of its previous state, whereupon the input to the acceptanceoutput latch LAOUT (via the gate NANDI) goes HIGH. The acceptance outputsignal QAOUT also rises to a “1”. This QAOUT value of “1” is thentransferred as a “1” to the input of the acceptance input latch LAINregardless of the state of the validation input signal QVIN. Theacceptance input signal QAIN then rises to a “1” at the next rising edgeof the clock signal PH1. Assuming that the validation signal IN_VALIDhas been correctly reset to a “0”, then upon the subsequent rising edgeof the clock signal PH0, the output from the validation latch LVIN willbecome a “0”, as it would have done if it had been reset directly.

[0371] As this example illustrates, it is only necessary to reset thevalidation latch in only one side of each stage (including the finalstage) in order to reset all validation latches. In fact, in manyapplications, it will not be necessary to reset every other validationlatch: If the reset signal NOTRESETO can be guaranteed to be low duringore than one complete cycle of both phases PH0, PH1 of the clock, thenthe “automatic reset” (a backwards propagation of the reset signal) willoccur for validation latches n preceding pipeline stages. Indeed, if thereset signal is held low for at least as many full cycles of both phasesof the clock as there are pipeline stages, it will only be necessary todirectly reset the validation output latch in the final pipeline stage.

[0372]FIGS. 5a and 5 b (referred to collectively as FIG. 5) illustrate atiming diagram showing the relationship between the non-overlappingclock signals PH0, PH1, the effect of the reset signal, and the holdingand transfer of data for the different permutations of validation andacceptance signals into and between the two illustrated sides of apipeline stage configured in the embodiment shown in FIG. 4. In theexample illustrated in the timing diagram of FIG. 5, it has been assumedthat the outputs from the data latches LIDIN, LDOUT are passed withoutfurther manipulation by intervening logic blocks B1, B2. This is by wayof example and not necessarily by way of limitation. It is to beunderstood that any combinatorial logic structures may be includedbetween the data latches of consecutive pipeline stages, or between theinput and output sides of a single pipeline stage. The actualillustrated values for the input data (for example the HEX data words“aa” or “04”) are also merely illustrative. As is mentioned above, theinput data bus nay have any width (and may even be analog), as long asthe data latches or other storage devices are able to accommodate andlatch or store each bit or value of the input word.

[0373] Preferred Data Structure—“Tokens”

[0374] In the sample application shown in FIG. 4, each stage processesall input data, since there is no control circuity that excludes anystage from allowing input data to pass through its combinatorial logicblock B1, B2, and so forth. To provide greater flexibility, the presentinvention includes a data structure in which “tokens” are used todistribute data and control information throughout the system. Eachtoken consists of a series of binary bits separated into one or moreblocks of token words. Furthermore, the bits fall into one of threetypes: address bits (A), data bits (D), or an extension bit (E). Assumeby way of example and, not necessarily by way of limitation, that datais transferred as words over an 8-bit bus with a 1-bit extension bitline. An example of a four-word token is, in order of transmission:First word: E A A A D D D D D Second word: E D D D D D D D D Third word:E D D D D D D D D Fourth word: E D D D D D D D D

[0375] Note that the extension bit E is used as an addition (preferably)to each data word. In addition, the address field can be of variablelength and is preferably transmitted just after the extension bit of thefirst word.

[0376] Tokens, therefore, consist of one or more words of (binary)digital data in the present invention. Each of these words istransferred in sequence and preferably in parallel, although this methodof transfer is not necessary; serial data transfer is also possibleusing known techniques. For example, in a video parser, controlinformation is transmitted in parallel, whereas data is transmittedserially.

[0377] As the example illustrates, each token has, preferably at thestart, an address field (the string of A-bits) that identifies the typeof data that is contained in the token. In most applications, a singleword or portion of a word is sufficient to transfer the entire addressfield, but this is not necessary in accordance with the invention, solong as logic circuitry is included in the corresponding pipeline stagesthat is able to store some representation of partial address fields longenough for the stages to receive and decode the entire address field.

[0378] Note that no dedicated wires or registers are required totransmit the address field. It is transmitted using the data bits. As isexplained below, a pipeline stage will not be slowed down if it is notintended to be activated by the particular address field, i.e., thestage will be able to pass along the token without delay.

[0379] The remainder of the data in the token following the addressfield is not constrained by the use of tokens. These D-data bits maytake on any values and the meaning attached to these bits is of noimportance here. That is, the meaning of the data can vary, for example,depending upon where the data is positioned within the system at aparticular point in time. The number of data bits D appended after theaddress field can be as long or as short as required, and the number ofdata words in different tokens may vary greatly. The address field andextension bit are used to convey control signals to the pipeline stages.Because the number of words in the data field (the string of D bits) canbe arbitrary, as can be he information conveyed in the data field canalso vary accordingly. The explanation below is, therefore, directed tothe use of the address and extension bits.

[0380] In the present invention, tokens are a particularly useful datastructure when a number of blocks of circuitry are connected together ina relatively simple configuration. The simplest configuration is apipeline of processing steps. For example, in the one shown in FIG. 1.The use of tokens, however, is not restricted to use on a pipelinestructure.

[0381] Assume once again that each box represents a complete pipelinestage. In the pipeline of FIG. 1, data flows from left to right in thediagrams Data enters the machine and passes into processing Stage A.This may or may not modify the data and it then passes the data to stageB. The modification, if any, may be arbitrarily complicated and, ingeneral, there will not be the same number of data items flowing intoany stage as flow out. Stage B modifies the data again and passes itonto Stage C, and so forth. In a scheme such as this, it is impossiblefor data to flow in the opposite direction, so that, for example, StageC cannot pass data to Stage A. This restriction is often perfectlyacceptable.

[0382] On the other hand, it is very desirable for Stage A to be able tocommunicate information to Stage C even though there is no directconnection between the two blocks. Stage A and C communication is onlyvia Stage B. One advantage of the tokens is their ability to achievethis kind of communication. Since any processing stage that does notrecognize a token simply passes it on unaltered to the next block.

[0383] According to this example, an extension bit is transmitted alongwith the address and data fields in each token so hat a processing stagecan pass on a token (which can be of arbitrary length) without having todecode its address at all. According to this example, any token in whichthe extension bit is HIGH (a “1”) is followed by a subsequent word whichis part of the same token. This word also has an extension bit, whichindicates whether there is a further token word in the token. When astage encounters a token word whose extension bit is LOW (a “0”), it isknown to be the last word of the token. The next word is then assumed tobe the first word of a new token.

[0384] Note that although the simple pipeline of processing stages isparticularly useful, it will be appreciated that tokens may be appliedto more complicated configurations o processing elements. An example ofa more complicated processing element is described below.

[0385] It is not necessary, in accordance with the present invention, touse the state of the extension bit to signal the last word of a giventoken by giving it an extension bit set to “0”. One alternative to thepreferred scheme is to move the extension bit so that it indicates thefirst word of a token instead of the last. This can be accomplished withappropriate changes in the decoding hardware.

[0386] The advantage of using the extension bit of the present inventionto signal the last word in a token rather than the first, is that it isoften useful to modify the behavior of a block of circuitry dependingupon whether or not a token has extension bits. An example of this is atoken that activates a stage that processes video quantization valuesstored in a quantization table (typically a memory device). For example,a table containing 64 eight-bit arbitrary binary integers.

[0387] In order to load a new quantization table into the quantizerstage of the pipeline, a “QUANT_TABLE” token is sent to the quantizer.In such a case the token, for example, consists of 65 token words. Thefirst word contains the code “QUANT_TABLE”, i.e., build a quantizationtable. This is followed by 64 words, which are the integers of thequantization table.

[0388] When encoding video data, it is occasionally necessary totransmit such a quantization table. In order to accomplish thisfunction, a QUANT_TABLE token with no extension words can be sent to thequantizer stage. On seeing this token, and noting that the extension bitof its first word is LOW, the quantizer stage can read out itsquantization table and construct a QUANT_TABLE token which includes the64 quantization table values. The extension bit of the first word (whichwas LOW) is changed so that it is HIGH and the token continues, withHIGH extension bits, until the new end of the token, indicated by a LOWextension bit on the sixty fourth quantization table value. Thisproceeds in the typical Dab through the system and is encoded into thebit stream.

[0389] Continuing with the example, the quantizer may either load a newquantization table into its own memory device or read out its tabledepending on whether the first word of the QUANT_TABLE token has itsextension bit set or not.

[0390] The choice of whether to use the extension bit to signal thefirst or last token word in a token will, therefore, depend on thesystem in which the pipeline will be used.

[0391] Both alternatives are possible in accordance with the invention.

[0392] Another alternative to the preferred extension bit scheme is toinclude a length count at the start of the token. Such an arrangementmay, for example, be efficient if a token is very long. For example,assume that a typical token in a given application is 1000 words long.Using the illustrated extension bit scheme (with the bit attached toeach token word) the token would require 1000 additional bits to containall the extension bits. However, only ten bits would be required toencode the token length in binary form.

[0393] Although there are, therefore, uses for long tokens, a experiencehas shown that there are many uses for short tokens. Here the preferredextension bit scheme is advantageous. If a token is only one word long,then only one bit is required to signal this. However, a counting schemewould typically require the same ten bits as before.

[0394] Disadvantages of a length count scheme include the following: 1)it is inefficient for short tokens; 2) places a maximum lengthrestriction on a token (with only en bits, no more than 1023 words canbe counted); 3) the length of a token must be known in advance ofgenerating the count (which is presumably at the start of the token); 4)every block of circuitry that deals with tokens would need to beprovided with hardware to count words; and 5) if the count should getcorrupted (due to a data transmission error) it is not clear whetherrecovery can be achieved.

[0395] The advantages of the extension bit scheme in accordance with thepresent invention include: 1) pipeline stages need not include a blockof circuitry that decodes every token since unrecognized tokens can bepassed on correctly by considering only the extension bit; 2) the codingof the extension bit is identical for all tokens; 3) there is no limitplaced on the length of a token; 4) the scheme is efficient (in terms ofoverhead to represent the length of the token) for short tokens; and 5)error recovery is naturally achieved. If an extension bit is corruptedthen one random token will be generated (for an extension bit corruptedfrom “1” to “0”) or a token will be lost (extension bit corrupted “0” to“1”). Furthermore, the problem is localized to the tokens concerned.After that token, correct operation is resumed automatically.

[0396] In addition, the length of the address field may be varied. Thisis highly advantageous since it allows the most common tokens to besqueezed into the minimum number of words. This, in turn, is of greatimportance in video data pipeline systems since it ensures that allprocessing stages can be continuously running at full bandwidth.

[0397] In accordance to the present invention, in order to allowvariable length address fields, the addresses are chosen so that a shortaddress followed by random data can never be confused with a longeraddress. The preferred technique for encoding the address field (whichalso serves as the “code” for activating an intended pipeline stage) isthe well-known technique first described by Huffman, hence the commonname “Huffman Code”. Nevertheless, it will be appreciated be one ofordinary skill in the art, that other coding schemes may also besuccessfully employed.

[0398] Although Huffman encoding is well understood in the field ofdigital design, the following example provides a general background:

[0399] Huffman codes consist of words made up of a string of symbols (inthe context of digital systems, such as the present invention, thesymbols are usually binary digits). The code words may have variablelength and the special property of Huffman code words is that a codeword is chosen so that none of the longer code words start with thesymbols that form a shorter code word. In accordance with the invention,token address fields are preferably (although not necessarily) chosenusing known Huffman encoding techniques.

[0400] Also in the present invention, the address field preferablystarts in the most significant bit (MSB) of the first word token. (Notethat the designation of the MSB is arbitrary and that this scheme can bemodified to accommodate various designations of the MSB.) The addressfield continues through contiguous bits of lesser significance. If, in agiven application, a token address requires more than one token word,the least significant bit in any given word the address field willcontinue in the most significant bit of the next word. The minimumlength of the address field is one bit.

[0401] Any of several known hardware structures can be used to generatethe tokens used in the present invention. One such structure is amicroprogrammed state machine. However, known microprocessors or otherdevices may also be used.

[0402] The principle advantage of the token scheme in accordance withthe present invention, is its adaptability to unanticipated needs. Forexample, if a new token is introduced, it is most likely that this willaffect only a small number of pipeline stages. The most likely case isthat only two stages or blocks of circuitry are affected, i.e., the oneblock that generates the tokens in the first place and the block orstage that has been newly designed or modified to deal with this newtoken. Note that it is not necessary to modify any other pipelinestages. Rather, these will be able to deal with the new token withoutmodification to their designs because they will not recognize it andwill, accordingly, pass that token on unmodified.

[0403] This ability of the present invention to leave substantiallyexisting designed devices unaffected has clear advantages. It may bepossible to leave some semiconductor chips in a chip set completelyunaffected by a design improvement in some other chips in the set. Thisis advantageous both from the perspective of a customer and from that ofa chip manufacturer. Even if modifications mean that all chips areaffected by the design change (a situation that becomes increasinglylikely as levels of integration progress so that the number of chips ina system drops) there will still be the considerable advantage of bettertime-to-market than can be achieved, since the same design can bereused.

[0404] In particular, note the situation that occurs when it becomesnecessary to extend the token set to include two word addresses. Even inthis case, it is still not necessary to modify an existing design. Tokendecoders in the pipeline stages will attempt to decode the first word ofsuch a token and will conclude that it does not recognize the token. Itwill then pass on the token unmodified using the extension bit toperform this operation correctly. It will not attempt to decode thesecond word of the token (even though this contains address bits)because it will “assume” that the second word is part of the data fieldof a token that it does not recognize.

[0405] In many cases, a pipeline stage or a connected block of circuitrywill modify a token. This usually, but not necessarily, takes the formof modifying the data field of a token. In addition, it is common forthe number of data words in the token to be modified, either by removingcertain data words or by adding new ones. In some cases, tokens areremoved entirely from the token stream.

[0406] In most applications, pipeline stages will typically only decode(be activated by) a few tokens; the stage does not recognize othertokens and passes them on unaltered. In a large number of cases, onlyone token is decoded, the DATA Token word itself.

[0407] In many applications, the operation of a particular stage willdepend upon the results of its own past operations. The “state” of thestage, thus, depends on its previous states. In other words, the stagedepends upon stored state information, which is another way of saying itmust retain some information about its own history one or more clockcycles ago. The present invention is well-suited for use in pipelinesthat include such “state machine” stages, as well as for use inapplications in which the latches in the data path are simple pipelinelatches.

[0408] The suitability of the two-wire interface, in accordance with thepresent invention, for such “state machine” circuits is a significantadvantage of the invention. This is especially true where a data path isbeing controlled by a state machine. In this case, the two-wireinterface technique above-described may be used to ensure that the“current state” of the machine stays in step with the data which it iscontrolling in the pipeline.

[0409]FIG. 6 shows a simplified block diagram of one example ofcircuitry included in a pipeline stage for decoding a token addressfield. This illustrates a pipeline stage that has the characteristics ofa “state machine”. Each word of a token includes an “extension bit”which is HIGH if there are more words in the token or LOW if this is thelast word of the token. If this is the last word of a token, the nextvalid data word is the start of a new token and, therefore, its addressmust be decoded. The decision as to whether or not to decode the tokenaddress in any given word, thus, depends upon knowing the value of theprevious extension bit.

[0410] For the sake of simplicity only, the two-wire interface (with theacceptance and validation signals and latches) is not illustrated andall details dealing with resetting the circuit are omitted. As before,an 8-bit data word is assumed by way of example only and not by way oflimitation.

[0411] This exemplifying pipeline stage delays the data bits and theextension bit by one pipeline stage. It also decodes the DATA Token. Atthe point when the first word of the DATA Token is presented at theoutput of the circuit, the signal “DATA_ADDR” is created and set HIGH.The data bits are delayed by the latches LDIN and LDOUT, each of whichis repeated eight times for the eight data bits used in this example(corresponding to an 8-input, 8-output latch). Similarly, the extensionbit is delayed by extension bit latches LEIN and LEOUT.

[0412] In this example, the latch LEPREV is provided to store the mostrecent state of the extension bit. The value of the extension bit isloaded into LEIN and is then loaded into LEOUT on the next rising edgeof the non-overlapping clock phase signal PH1. Latch LEOUT, thus,contains the value of the current extension bit, but only during thesecond half of the non-overlapping, two-phase clock. Latch LEPREV,however, loads this extension bit value on the next rising edge of theclock signal PH0, that is, the same signal that enables the extensionbit input latch LEIN. The output QEPREV of the latch LEPREV, thus, willhold the value of the extension bit during the previous PH0 clock phase.

[0413] The five bits of the data word output from the inverting Qoutput, plus the non-inverted MD[2], of the latch LDIN are combined withthe previous extension bit value QEPREV in a series of logic gatesNAND1, NAND2, and NOR1, whose operations are well known in the art ofdigital design. The designation “N_MD[m] indicates the logical inverseof bit n of the mid-data word MD(7:0) . Using known techniques ofBoolean algebra, it can be shown that the output signal SA from thislogic block (the output from NOR1) is HIGH (a “1” ) only when theprevious extension bit is a “0” (QPREV=“0”) and the data word at theoutput of the non-inverting Q latch (the original input word) LDIN hasthe structure “000001xx”, that is, the five high-order bits MD∂7]-MD[3]bits are all “0” and the bit MD[2] is a “1” and the bits in the Zero-onepositions have any arbitrary value.

[0414] There are, thus, four possible data words (there are fourpermutations of “xx”) that will cause SA and, therefore, the output ofthe address signal latch LADDR to whose input SA is connected, to becomeHIGH. In other words, this stage provides an activation signal(DATA_ADDR=“1”) only when one of the four possible proper tokens ispresented and only when the previous extension bit was a zero, that is,the previous data word was the last word in the previous series of tokenwords, which means that the current token word is the first one in thecurrent token.

[0415] When the signal QPREV from latch LEPREV is LOW, the value at theoutput of the latch LDIN is therefore the first word of a new token. Thegates NAND1, NAND2 and NOR1 decode the DATA token (000001xx). Thisaddress decoding signal SA is, however, delayed in latch LADOR so thatthe signal DATA_ADOR has the same timing as the output data OUT_DATA andOUT_EXTN.

[0416]FIG. 7 is another simple example of a state-dependent pipelinestage in accordance with the present invention, which generates thesignal LAST_OUT_EXTN to indicate the value of the previous outputextension bit OUT_EXTN. One of the two enabling signals (at the CKinputs) to the present and last extension bit latches, LEOUT and LEPREV,respectively, is derived from the gate AND1 such that these larches onlyload a new value for them when the data is valid and is being accepted(the Q outputs are HIGH from the output validation and acceptancelatches LVOUT and LAOUT, respectively). In this way, they only holdvalid extension bits and are not loaded with spurious values associatedwith data that is not valid. In the embodiment shown in FIG. 7, thetwo-wire valid/accept logic includes the OR1 and OR2 gates with inputsignals consisting of the downstream acceptance signals and theinverting output of the validation latches LVIN and LVOUT, respectively.This illustrates one Way in which the gates NAND1/2 and INV1/2 in FIG. 4can be replaced if the latches have inverting outputs.

[0417] Although this is an extremely simple example of a“state-dependent” pipeline stage, i.e., since it depends on the state ofonly a single bit, it is generally true that all latches holding stateinformation will be updated only when data is actually transferredbetween pipeline stages. In other words, only when the data is bothvalid and being accepted by the next stage. Accordingly, care must betaken to ensure that such latches are properly reset.

[0418] The generation and use of tokens in accordance with the presentinvention, thus, provides several advantages over known encodingtechniques for data transfer through a pipeline.

[0419] First, the tokens, as described above, allow for variable lengthaddress fields (and can utilize Huffman coding for example) to provideefficient representation of common tokens.

[0420] Second, consistent encoding of the length of a token allows theend of a token (and hence the start of the next token) to be processedcorrectly (including simple non-manipulative transfer), even if thetoken is not recognized by the token decoder circuitry in a givenpipeline stage.

[0421] Third, rules and hardware structures for the handling ofunrecognized tokens (that is, for passing them on unmodified allowcommunication between one stage and a downstream stage that is not itsnearest neighbor in the pipeline. This also increases the expandabilityand efficient adaptability of the pipeline since it allows for futurechanges in the token set Without requiring large scale redesigning ofexisting pipeline stages. The tokens of the present invention areparticularly useful when used in conjunction with the two-wire interfacethat is described above and below.

[0422] As an example of the above, FIGS. 8a and 8 b, taken together (andreferred to collectively below as FIG. 8) depict a block diagram of apipeline stage whose function is as follows. If the stage is processinga predetermined token (known in this example as the DATA token), then itwill duplicate every word in this token with the exception of the firstone, which includes the address field of the DATA token. If, on theother hand, the stage is processing any other kind of token, it willdelete every word. The overall effect is that, at the output, only DATATokens appear and each word within these tokens is repeated twice.

[0423] Many of the components of this illustrated system may be the sameas those described in the much simpler structures shown in FIGS. 4, 6,and 7. This illustrates a significant advantage. More complicatedpipeline stages will still enjoy the same benefits of flexibility andelasticity, since the sane two-wire interface may be used with little orno adaptation.

[0424] The data duplication stage shown in FIG. 8 is merely one exampleof the endless number of different types of operations that a pipelinestage could perform in any given application. This “duplication stage”illustrates, however, a stage that can form a “bottleneck”, so that thepipeline according to this embodiment will “pack together”.

[0425] A “bottleneck” can be any stage that either takes a relativelylong time to perform its operations, or that creates more data in thepipeline than it receives. This example also illustrates that thetwo-wire accept/valid interface according to this embodiment can beadapted very easily to different applications.

[0426] The duplication stage shown in FIG. 8 also has two latches LIENand LEOUT that, as in the example shown in FIG. 6, latch the state ofthe extension bit at the input and at the output of the stage,respectively. As FIG. 8a shows, the input extension latch LEIN isclocked synchronously with the input data latch LDIN and the validationsignal IN_VALID.

[0427] For ease of reference, the various latches included in theduplication stage are paired below with their respective output signals:

[0428] In the duplication stage, the output from the data latch LDINforms intermediate data referred to as MID_DATA. This intermediate dataword is loaded into the data output latch LDOUT only when anintermediate acceptance signal (labeled “MID_ACCEPT” in FIG. 8a) is setHIGH.

[0429] The portion of the circuitry shown in FIG. 8 below the acceptancelatches LAIN, LAOUT, shows the circuits that are added to the basicpipeline structure to generate the various internal control signals usedto duplicate data. These include a “DATA_TOKEN” signal that indicatesthat the circuitry is currently processing a valid DATA Token, and aNOT_DUPLICATE signal which is used to control duplication of data. Whenthe circuitry is processing a DATA Token, the NOT_DUPLICATE signaltoggles between a HIGH and a LOW state and this causes each word in thetoken to be duplicated once (but no more times). When the circuitry isnot processing a valid DATA Token then the NOT_DUPLICATE signal is heldin a HIGH state. Accordingly, this means that the token words that arebeing processed are not duplicated.

[0430] As FIG. 8a illustrates, the upper six bits of 8-bit intermediatedata word and the output signal QI1 from the latch LI1 form inputs to agroup of logic gates NOR1, NOR2, NAND18. The output signal from the gateNAND18 is labeled S1. Using well-known Boolean algebra, it can be shownthat the signal S1 is a “0” only when the output signal QI1 is a “1” andthe MID DATA word has the following structure: “000001xx”, that is, theupper five bits are all “0”, the bit MID_DATA[2] is a “1” and the bitsin the MID_DATA[1] and MID_DATAC[0] positions have any arbitrary value.Signal S1, therefore, acts as a “token identification signal” which islow only when the MID_DATA signal has a predetermined structure and theoutput from the latch LI1 is a “1”. The nature of the latch LI1 and itsoutput QI1 is explained further below.

[0431] Latch LO1 performs the function of latching the last value of theintermediate extension bit (labeled “MID_EXTN” and as signal S4), and itloads this value on the next rising edge of the clock phase PH0 into thelatch LI1, whose output is the bit QI1 and is one of the inputs to thetoken decoding logic group that forms signal S1. Signal S1, as isexplained above, may only drop to a “0” if the signal QI1 is a “1” (andthe MID_DATA signal has the predetermined structure). Signal S1 may,therefore, only drop to a “0” whenever the last extension bit was “0”,indicating that the previous token has ended. Therefore, the MID_DATAword is the first data word in a new token.

[0432] The latches LO2 and LI2 together with the NAND gates NAND20 andNAND22 form storage for the signal, DATA_TOKEN. In the normal situation,the signal QI1 at the input to NAND20 and the signal S1 at the input toNAND22 will both be at logic “1”. It can be shown, again by thetechniques of Boolean algebra, that in this situation these NAND gatesoperate in the same manner as inverters, that is, the signal QI2 fromthe output of latch LI2 is inverted in NAND20 and then this signal isinverted again by NAND22 to form the signal 52. In this case, sincethere are two logical inversions in this path, the signal S2 will havethe same value as QI2.

[0433] It can also be seen that the signal DATA TOKEN at the output oflatch LO2 forms the input to latch LI2. As a result, as long as thesituation remains in which both QI1 and S1 are HIGH, the signalDATA_TOKEN will retain its state (whether “0” or “1”). This is true eventhough the clock signals PH0 and PH0 are clocking the latches (LI2 andLO2 respectively). The value of DATA_TOKEN can only change when one orboth of the signals QI1 and S1 are “0”.

[0434] As explained earlier, the signal QI1 will be “0” when theprevious extension bit was “0”. Thus, it will be “0” whenever theMID_DATA value is the first word of a token (and, thus, includes theaddress field for the token). In this situation, the signal S1 may beeither “0” or “1”. As explained earlier, signal S1 will be “0” if theMID_DATA word has the predetermined structure that in this exampleindicates a “DATA” Token. If the MID_DATA word has any other structure,(indicating that the token is some other token, not a DATA Token), S1will be “1”.

[0435] If QI1 is “0” and S1 is “1”, this indicates there is some tokenother than a DATA Token. As is well known in the field of digitalelectronics, the output of NAND20 will be “1”. The NAND gate NAND22 willinvert this (as previously explained) and the signal 52 will thus be a“0”. As a result, this “0” value will be loaded into latch LO2 at thestart of the next PH1 clock phase and the DATA TOKEN signal will become“0”, indicating that the circuitry is not processing a DATA token.

[0436] If QI1 is “0” and SO is “0”, thereby indicating a DATA token,then the signal S2 will be “1” (regardless of the other input to NAND22from the output of NAND20). As a result, this “1” value will be loadedinto latch LO2 at the start of the next PH1 clock phase and theDATA_TOKEN signal will become “1”, indicating that the circuitry isprocessing a DATA token.

[0437] The NOT_DUPLICATE signal (the output signal QO3) is similarlyloaded into the latch LI3 on the next rising edge of the clock PH0. Theoutput signal QI3 from the latch LI3 is combined with the output signalQI2 in a gate NAND24 to form the signal 53. As before, Boolean algebracan be used to show that the signal S3 is a “0” only when both of thesignals QI2 and QI3 have the value “1”. If the signal QI2 becomes a “0”,that is, the DATA TOKEN signal is a “0”, then the signal S3 becomes a“1”. In other words, if there is not a valid DATA TOKEN (QI2=0) or thedata word is not a duplicate (QI3=0), then the signal 53 goes high.Assume now, that the DATA TOKEN signal remains HIGH for more than oneclock signal. Since the NOT_DUPLICATE signal (QO3) is “fed back” to thelatch LI3 and will be inverted by the gate NAND 24 (since its otherinput QI2 is held HIGH), the output signal QO3 will toggle between “0”and “1”. If there is no valid DATA Token, however, the signal QI2 willbe a “0”, and the signal 53 and the output QO3, will be forced HIGHuntil the DATE_TOKEN signal once again goes to a “1”.

[0438] The output QO3 (the NOTDUPLICATE signal) is also fed back and iscombined with the output QA1 from the acceptance latch LAIN in a seriesof logic gates (NAND16 and INV16, which together form an AND gate) thathave as their output a “1”, only when the signals QA1 and QO3 both havethe value “1”. As FIG. 8a shows, the output from the AND gate (the gateNAND16 followed by the gate INV16) also forms the acceptance signal,IN_ACCEPT, which is used as described above in the two-wire interfacestructure.

[0439] The acceptance signalIN_(—ACCEPT is also used as an enabling signal to the latches LDIN, LEIN, and LVIN. As a result, if the NOT)_DUPLICATEsignal is low, the acceptance signal IN_ACCEPT will also be low, and allthree of these latches will be disabled and will hold the values storedat their outputs. The stage will not accept new data until theNOT_DUPLICATE signal becomes HIGH. This is in addition to therequirements described above for forcing the output from the acceptancelatch LAIN high.

[0440] As long as there is a valid DATA_TOKEN (the DATA_TOKEN signal QO2is a “1”), the signal QO3 will toggle between the HIGH and LOW states,so that the input latches will be enabled and will be able to acceptdata, at most, during every other complete cycle of both clock phasesPH0, PH1. The additional condition that the following stage be preparedto accept data, as indicated by a “HIGH”OUT_(—ACCEPT signal, must, of course, still be satisfied. The output latch LDOUT will, therefore, place the same data word onto the output bus OUT)_DATAfor at least two full clock cycles. TheOUT_(—VALID signal will be a “1” only when there is both a valid DATA)_TOKEN(QO2 HIGH) and the validation signal QVOUT is HIGH.

[0441] The signal QEIN, which is the extension bit corresponding toMID_DATA, is combined with the signal S3 in a series of logic gates(INV10 and NAND10) to form a signal S4. During presentation of a DATAToken, each data word MID_DATA will be repeated by loading it into theoutput latch LDOUT twice. During the first of these, S4 will be forcedto a “1” by the action of NAND10. The signal S4 is loaded in the latchLEOUT to form OUTEXTN at the same time as MID_DATA is loaded into LDOUTto form OUT_DATA[7:0].

[0442] Thus, the first time a given MID_DATA is loaded into LEOUT, theassociated OUTEXTN will be forced high, whereas, on the second occasion,OUTEXTN will be the same as the signal QEIN. Now consider the situationduring the very last word of a token in which QEIN is known to be low.During the first time MID_DATA is loaded into LDOUT, OUTEXTN will be“1”, and during the second time, OUTEXTN will be “0”, indicating thetrue end of the token.

[0443] The output signal QVIN from the validation latch LVIN is combinedwith the signal QI3 in a similar gate combination (INV12 and NAND12) toform a signal S5. Using known Boolean techniques, it can be shown thatthe signal S5 is HIGH either when the validation signal QVIN is HIGH, orwhen the signal QI3 is low (indicating that the data is a duplicate).The signal S5 is loaded into the validation output latch LVOUT at thesame time that MID_DATA is loaded into LDOUT and the intermediateextension bit (signal 54) is loaded into LEOUT. Signal 55 is alsocombined with the signal QO2 (the data token signal) in the logic gatesNAND30 and INV30 to form the output validation signal OUT VALID. As wasmentioned earlier, OUT VALID is HIGH only when there is a valid tokenand the validation signal QVOUT is high.

[0444] In the present invention, the MID_ACCEPT signal is combined withthe signal S5 in a series of logic gates (NAND26 and INV26) that performthe well-known AND function to form a signal S6 that is used as one ofthe two enabling signals to the latches LO1, LO2 and LO3. The signal 56rises to a “1” when the MID_ACCEPT signal is HIGH and when either thevalidation signal QVIN is high, or when the token is a duplicate (QI3 isa “0”). If the signal MID_ACCEPT is HIGH, the latches LO1-LO3 will,therefore, be enabled when the clock signal PH1 is high whenever validinput data is loaded at the input of the stage, or when the latched datais a duplicate.

[0445] From the discussion above, one can see that the stage shown inFIGS. 8a and 8 b will receive and transfer data between stages under thecontrol of the validation and acceptance signals, as in previousembodiments, with the exception that the output signal from theacceptance latch LAIN at the input side is combined with the togglingduplication signal so that a data word will be output twice before a newword will be accepted.

[0446] The various logic gates such as NAND16 and INV16 may, of course,be replaced by equivalent logic circuitry (in this case, a single ANDgate). Similarly, if the latches LEIN and LVIN, for example, haveinverting outputs, the inverters INV10 and INV12 will not be necessary.Rather, the corresponding input to the gates NAND10 and NAND12 can betied directly to the inverting outputs of these latches. As long as theproper logical operation is performed, the stage will operate in thesame manner. Data words and extension bits will still be duplicated.

[0447] One should note that the duplication function that theillustrated stage performs will not be performed unless the first dataword of the token has a “1” in the third position of the word and “O's”in the five high-order bits. (Of course, the required pattern can easilybe changed and set by selecting other logic gates and interconnectionsother than the NOR1, NOR2, NND18 gates shown.)

[0448] In addition, as FIG. 8 shows, the OUT_VALID signal will be forcedlow during the entire token unless the first data word has the structuredescribed above. This has the effect that all tokens except the one thatcauses the duplication process will be deleted from the token stream,since a device connected to the output terminals (OUTDATA, OUTEXTN andOUTVALID) will not recognize these token words as valid data.

[0449] As before, both validation latches LVIN, LVOUT in the stage canbe reset by a single conductor NOT_RESETO, and a single resetting inputR on the downstream latch LVOUT, with the reset signal being propagatedbackwards to cause the upstream validation latch to be forced low on thenext clock cycle.

[0450] It should be noted that in the example shown in FIG. 8, theduplication of data contained in DATA tokens serves only as an exampleof the way in which circuitry may manipulate the ACCEPT and VALIDsignals so that more data is leaving the pipeline stage than that whichis arriving at the input. Similarly, the example in FIG. 8 removes allnon-DATA tokens purely as an illustration of the way in which circuitrymay manipulate the VALID signal to remove data from the stream. In mosttypical applications, however, a pipeline stage will simply pass on anytokens that it does not recognize, unmodified, so that other stagesfurther down the pipeline may act upon them if required.

[0451]FIGS. 9a and 9 b taken together illustrate an example of a timingdiagram for the data duplication circuit shown in FIGS. 5a and 8 b. Asbefore, the timing diagram shows the relationship between the two-phaseclock signals, the various internal and external control signals, andthe manner in which data is clocked between the input and output sidesof the stage and is duplicated.

[0452] Referring now more particularly to FIG. 10, there is shown areconfigurable process stage in accordance with one aspect of thepresent invention.

[0453] Input latches 34 receive an input over a first bus 31. A firstoutput from the input latches 34 is passed over line 32 to a tokendecode subsystem 33. A second output from the input latches 34 is passedas a first input over line 35 to a processing unit 36. A first outputfrom the token decode subsystem 33 is passed over line 37 as a secondinput to the processing unit 36. A second output from the token decode33 is passed over line 40 to an action identification unit 39. Theaction identification unit 39 also receives input from registers 43 and44 over line 46. The registers 43 and 44 hold the state of the machineas a whole. This state is determined by the history of tokens previouslyreceived. The output from the action identification unit 39 is passedover line 38 as a third input to the processing unit 36. The output fromthe processing unit 36 is passed to output latches 41. The output fromthe output latches 41 is passed over a second bus 42.

[0454] Referring now to FIG. 11, a Start Code Detector (SCD) 51 receivesinput over a two-wire interface 52. This input can be either in the formof DATA tokens or as data bits in a data stream. A first output from theStart Code Detector 51 is passed over line 53 to a first logicalfirst-in first-out buffer (FIFO) 54. The output from the first FIFO 54is logically passed over line 55 as a first input to a Huffman decoder56. A second output from the Start Code Detector 51 is passed over line57 as a first input to a DRAM interface 58. The DRAM interface 58 alsoreceives input from a buffer manager 59 over line 60. Signals aretransmitted to and received from external DRAM (not shown) by the DRAMinterface 58 over line 61. A first output from the DRAM interface 58 ispassed over line 62 as a first physical input to the Huffman decoder 56.

[0455] The output from the Huffman decoder 56 is passed over line 63 asan input to an Index to Data Unit (ITOD) 64. The Huffman decoder 56 andthe ITOD 64 work together as a single logical unit. The output from theITOD 64 is passed over line 65 to an arithmetic logic unit (ALU) 66. Afirst output from the ALU 66 is passed over line 67 to a read-onlymemory (ROM) state machine 68. The output from the ROM state machine 68is passed over line 69 as a second physical input to the Huffman decoder56. A second-output from the ALU 66 is passed over line 70 to a TokenFormatter (T/F) 71.

[0456] A first output 72 from the T/F 71 of the present invention ispassed over line 72 to a second FIFO 73. The output from the second FIFO73 is passed over line 74 as a first input to an inverse modeller 75. Asecond output from the T/F 71 is passed over line 76 as a third input tothe DRAM interface 58. A third output from the DRAM interface 58 ispassed over line 77 as a second input to the inverse modeller 75. Theoutput from the inverse modeller 75 is passed over line 78 as an inputto an inverse quantizer 79 The output from the inverse quantizer 79 ispassed over line 80 as an input to an inverse zig-zag (IZZ) 81. Theoutput from the IZZ 81 is passed over line 82 as an input to an inversediscrete cosine transform (IDCT) 83. The output from the IDCT 83 ispassed over line 84 to a temporal decoder (not shown).

[0457] Referring now more particularly to FIG. 12, a temporal decoder inaccordance with the present invention is shown. A fork 91 receives asinput over line 92 the output from the IDCT 83 (shown in FIG. 11). As afirst output from the fork 91, the control tokens, e.g., motion vectorsand the like, are passed over line 93 to an address generator 94. Datatokens are also passed to the address generator 94 for countingpurposes. As a second output from the fork 91, the data is passed overline 95 to a FIFO 96. The output from the FIFO 96 is then passed overline 97 as a first input to a summer 98. The output from the addressgenerator 94 is passed over line 99 as a first input to a DRAM interface100. signals are transmitted to and received from external DRAM (notshown) by the DRAM interface 100 over line 101. A first output from theDRAM interface 100 is passed over line 102 to a prediction filter 103.The output from the prediction filter 103 is passed over line 104 as asecond input to the summer 98. A first output from the summer 98 ispassed over line 105 to output selector 106. A second output from thesummer 98 is passed over line 107 as a second input to the DRAMinterface 100. A second output from the DRAM interface 100 is passedover line 108 as a second input to the output selector 106. The outputfrom the output selector 106 is passed over line 109 to a VideoFormatter (not shown in FIG. 12).

[0458] Referring now to FIG. 13, a fork 111 receives input from theoutput selector 106 (shown in FIG. 12) over line 112. As a first outputfrom the fork 111, the control tokens are passed over line 113 to anaddress generator 114. The output from the address generator 114 ispassed over line 115 as a first input to a DRAM interface 116. As asecond output from the fork 111 the data is passed over line 117 as asecond input to the DRAM interface 116. Signals are transmitted to andreceived from external DRAM (not shown) by the DRAM interface 116 overline 118. The output from the DRAM interface 116 is passed over line 119to a display pipe 120.

[0459] It will be apparent from the above descriptions that each linemay comprise a plurality of lines, as necessary.

[0460] Referring now to FIG. 14a, in the MPEG standard a picture 131 isencoded as one or more slices 132. Each slice 132 is, in turn, comprisedof a plurality of blocks 133, and is encoded row-by-row, left-to-rightin each row. As is shown, each slice 132 may span exactly one full lineof blocks 133, less than one line B or D of blocks 133 or multiple linesC of blocks 133.

[0461] Referring to FIG. 14b, in the JPEG and H.261 standards, theCommon Intermediate Format (CIF) is used, wherein a picture 141 isencoded as 6 rows each containing 2 groups of blocks (GOBs) 142. EachGOB 142 is, in turn, composed of either 3 rows or 6 rows of anindeterminate number of blocks 143. Each GOB 142 is encoded in a zigzagdirection indicated by the arrow 144. The GOBs 142 are, in turn,processed row-by-row, left-to-right in each row.

[0462] Referring now to FIG. 14c, it can be seen that, for both MPEG andCIF, the output of the encoder is in the form of a data stream 151. Thedecoder receives this data stream 151. The decoder can then reconstructthe image according to the format used to encode it. In order to allowthe decoder to recognize start and end points for each standard, thedata stream 151 is segmented into lengths of 33 blocks 152.

[0463] Referring to FIG. 15, a Venn diagram is shown, representing therange of values possible for the table selection from the Huffmandecoder 56 (shown in FIG. 11) of the present invention. The valuespossible for an MPEG decoder and an H.261 decoder overlap, indicatingthat a single table selection will decode both certain MPEG and certainH.261 formats. Likewise, the values possible for an MPEG decoder and aJPEG decoder overlap, indicating that a single table selection willdecode both certain MPEG and certain JPEG formats. Additionally, it isshown that the H.261 values and the JPEG values do not overlap,indicating that no single table selection exists that will decode bothformats.

[0464] Referring now more particularly to FIG. 16, there is shown aschematic representation of variable length picture data in accordancewith the practice of the present invention. A first picture 161 to beprocessed contains a first PICTURE_START token 162, first pictureinformation of indeterminate length 163, and a first PICTURE_END token164. A second picture 165 to be processed contains a secondPICTURE_START token 166, second picture information of indeterminatelength 167, and a second PICTURE_END token 168. The PICTURE_START tokens162 and 166 indicate the start of the pictures 161 and 165 to theprocessor. Likewise, the PICTURE_END tokens 164 and 168 signify the endof the pictures 161 and 165 to the processor. This allows the processorto process picture information 163 and 167 of variable lengths.

[0465] Referring to FIG. 17, a split 171 receives input over line 172. Afirst output from the split 171 is passed over line 173 to an addressgenerator 174. The address generated by the address generator 174 ispassed over line 175 to a DRAM interface 176. Signals are transmitted toand received from external DRAM (not shown) by the DRAM interface 176over line 177. A first output from the DRAM interface 176 is passed overline 178 to a prediction filter 179. The output from the predictionfilter 179 is passed over line 180 as a first input to a summer 181. Asecond output from the split 171 is passed over line 182 as an input toa first-in first-out buffer (FIFO) 183. The output from the FIFO 183 ispassed over line 184 as a second input to the summer 181. The outputfrom the summer 181 is passed over line 185 to a write signal generator186. A first output from the write signal generator 186 is passed overline 187 to the DRAM interface 176. A second output from the writesignal generator 186 is passed over line 188 as a first input to a readsignal generator 189. A second output from the DRAM interface 176 ispassed over line 190 as a second input to the read signal generator 189.The output from the read signal generator 189 is passed over line 191 toa Video Formatter (not shown in FIG. 17).

[0466] Referring now to FIG. 18, the prediction filtering process isillustrated. A forward picture 201 is passed over line 202 as a firstinput to a summer 203. A backward picture 204 is passed over line 205 asa second input to the summer 203. The output from the summer 203 ispassed over line 206.

[0467] Referring to FIG. 19, a slice 211 comprises one or moremacroblocks 212. In turn, each macroblock 212 comprises four luminanceblocks 213 and two chrominance blocks 214, and contains the informationfor an original 16×16 block of pixels. Each of the four luminance blocks213 and two chrominance blocks 214 is 8×8 pixels in size. The fourluminance blocks 213 contain a 1 pixel to 1 pixel mapping of theluminance (Y) information from the original 16—16 block of pixels. Onechrominance block 214 contains a representation of the chrominance levelof the blue color signal (Cu/b), and the other chrominance block 214contains a representation of the chrominance level of the red colorsignal (Cv/r). Each chrominance level is subsampled such that each 8×8chrominance block 214 contains the chrominance level of its color signalfor the entire original 16×16 block of pixels.

[0468] Referring now to FIG. 20, the structure and function of the StartCode Detector will become apparent. A value register 221 receives imagedata over a line 222. The line 222 is eight bits wide, allowing forparallel transmission of eight bits at a time. The output from the valueregister 221 is passed serially over line 223 to a decode register 224.A first output from the decode register 224 is passed to a detector 225over a line 226. The line 226 is twenty-four bits wide, allowing forparallel transmission of twenty-four bits at a time. The detector 225detects the presence or absence of an image which corresponds to astandard-independent start code of 23 “zero” values followed by a single“one” value. An 8-bit data value image follows a valid start code image.On detecting the presence of a start code image, the detector 225transmits a start image over a line 227 to a value decoder 228.

[0469] A second output from the decode register 224 is passed seriallyover line 229 to a value decode shift register 230. The value decodeshift register 230 can hold a data value image fifteen bits long. The8-bit data value following the start code image is shifted to the rightof the value decode shift register 230, as indicated by area 231. Thisprocess eliminates overlapping start code images, as discussed below. Afirst output from the value decode shift register 230 is passed to thevalue decoder 228 over a line 232. The line 232 is fifteen bits wide,allowing for parallel transmission of fifteen bits at a time. The valuedecoder 228 decodes the value image using a first look-up table (notshown). A second output from the value decode shift register 230 ispassed to the value decoder 228 which passes a flag to anindex-to-tokens converter 234 over a line 235. The value decoder 228also passes information to the index-to-tokens converter 234 over a line236. The information is either the data value image or start code indeximage obtained from the first look-up table. The flag indicates whichform of information is passed. The line 236 is fifteen bits wide,allowing for parallel transmission of fifteen bits at a time. While 15bits has been chosen here as the width in the present invention it willbe appreciated that bits of other lengths may also be used. Theindex-to-tokens converter 234 converts the information to token imagesusing a second look-up table (not shown) similar to that given in Table12-3 of the Users Manual. The token images generated by theindex-to-tokens converter 234 are then output over a line 237. The line237 is fifteen bits wide, allowing for parallel transmission of fifteenbits at a time.

[0470] Referring to FIG. 21, a data stream 241 consisting of individualbits 242 is input to a Start Code Detector (not shown in FIG. 21). Afirst start code image 243 is detected by the Start Code Detector. TheStart Code Detector then receives a first data value image 244. Beforeprocessing the first data value image 244, the Start Code Detector maydetect a second start code image 245, which overlaps the first datavalue image 244 at a length 246. If this occurs, the Start Code Detectordoes not process the first data value image 244, and instead receivesand processes a second data value image 247.

[0471] Referring now to FIG. 22, a flag generator 251 receives data as afirst input over a line 252. The line 252 is fifteen bits wide, allowingfor parallel transmission of fifteen bits at a time. The flag generator251 also receives a flag as a second input over a line 253, and receivesan input valid image over a first two-wire interface 254. A first outputfrom the flag generator 251 is passed over a line 255 to an input validregister (not shown). A second output from the flag generator 251 ispassed over a line 256 to a decode index 257. The decode index 257generates four outputs; a picture start image is passed over a line 258,a picture number image is passed over a line 259, an insert image ispassed over a line 260, and a replace image is passed over a line 261.The data from the flag generator 251 is passed over a line 262 a. Aheader generator 263 uses a look-up table to generate a replace image,which is passed over a line 262 b. An extra word generator 264 uses theMPU to generate an insert image, which is passed over a line 262 c. Line262 a, and line 262 b combine to form a line 262, which is first inputto output latches 265. The output latches 265 pass data over a line 266.The line 266 is fifteen bits wide, allowing for parallel transmission offifteen bits at a time.

[0472] The input valid register (not shown) passes an image as a firstinput to a first OR gate 267 over a line 268. An insert image is passedover a line 269 as a second input to the first OR gate 267. The outputfrom the first OR gate 267 is passed as a first input to a first ANDgate 270 over a line 271. The logical negation of a remove image ispassed over a line 272 as a second input to the first AND gate 270 ispassed as a second input to the output latches 265 over a line 273. Theoutput latches 265 pass an output valid image over a second two-wireinterface 274. An output accept image is received over the secondtwo-wire interface 274 by an output accept latch 275. The output fromthe output accept latch 275 is passed to an output accept register (notshown) over a line 276.

[0473] The output accept register (not shown) passes an image as a firstinput to a second OR gate 277 over a line 278. The logical negation ofthe output from the input valid register is passed as a second input tothe second OR gate 277 over a line 279. The remove image is passed overa line 280 as a third input to the second OR gate 277. The output fromthe second OR gate 277 is passed as a first input to a second AND gate281 over a line 282. The logical negation of an insert image is passedas a second input to the second AND gate 281 over a line 283. The outputfrom the second AND gate 281 is passed over a line 284 to an inputaccept latch 285. The output from the input accept latch 285 is passedover the first two-wire interface 254. TABLE 600 Format Image ReceivedTokens Generated 1. H.261 SEQUENCE START SEQUENCE START MPEG PICTURESTART GROUP START JPEG (None) PICTURE START PICTURE DATA 2. H.261 (None)PICTURE END MPEG (None) PADDING JPEG (None) FLUSH STOP AFTER PICTURE

[0474] As set forth in Table 600 which shows a relationship between theabsence or presence of standard signals in the certain machineindependent control tokens, the detection of an image by the Start CodeDetector 51 generates a sequence of machine independent Control Tokens.Each image listed in the “Image Received” column starts the generationof all machine independent control tokens listed in the group in the“Tokens Generated” column. Therefore, as shown in line 1 of Table 600,whenever a “sequence start” image is received during H.261 processing ora “picture start” image is received during MPEG processing, the entiregroup of four control tokens is generated, each followed by itscorresponding data value or values. In addition, as set forth at line 2of Table 600, the second group of four control tokens is generated atthe proper time irrespective of images received by the Start CodeDetector 51. TABLE 601 DISPLAY ORDER: I1 B2 B3 P4 B5 B6 P7 B8 B9 I10TRANSMIT ORDER: I1 P4 B2 B3 P7 B5 B6 I10 B8 B9

[0475] As shown in line 1 of Table 601 which shows the timingrelationship between transmitted pictures and displayed pictures, thepicture frames are displayed in numerical order. However, in order toreduce the number of frames that must be stored in memory, the framesare transmitted in a different order. It is useful to begin the analysisfrom an intraframe (I frame). The Il frame is transmitted in the orderit is to be displayed. The next predicted frame (P frame), P4, is thentransmitted. Then, any bi-directionally interpolated frames (B frames)to be displayed between the Il frame and P4 frame are transmitted,represented by frames B2 and B3. This allows the transmitted B frames toreference a previous frame (forward prediction) or a future frame(backward prediction). After transmitting all the B frames to bedisplayed between the Il frame and the P4 frame, the next P frame, P7,is transmitted. Next, all the B frames to be displayed between the P4and P7 frames are transmitted, corresponding to B5 and B6. Then, thenext I frame, 110, is transmitted. Finally, all the B frames to bedisplayed between the P7 and I10 frames are transmitted, correspondingto frames B8 and B9. This ordering of transmitted frames requires onlytwo frames to be kept in memory at any one time, and does not requirethe decoder to wait for the transmission of the next P frame or I frameto display an interjacent B frame.

[0476] Further information regarding the structure and operation, aswell as the features, objects and advantages, of the invention willbecome more readily apparent to one of ordinary skill in the art fromthe ensuing additional detailed description of illustrative embodimentof the invention which, for purposes of clarity and convenience ofexplanation are grouped and set forth in the following sections:

[0477] 1. Multi-Standard Configurations

[0478] 2. JPEG Still Picture Decoding

[0479] 3. Motion Picture Decompression

[0480] 4. RAM Memory Map

[0481] 5. Bitstream Characteristics

[0482] 6. Reconfigurable Processing Stage

[0483] 7. Multi-Standard Coding

[0484] 8. Multi-Standard Processing Circuit—2nd Mode of Operation

[0485] 9. Start Code Detector

[0486] 10. Tokens

[0487] 11. DRAM Interface

[0488] 12. Prediction Filter

[0489] 13. Accessing Registers

[0490] 14. Microprocessor Interface (MPI)

[0491] 15. MPI Read Timing

[0492] 16. MPI write Timing

[0493] 17. Key Hole Address Locations

[0494] 18. Picture End

[0495] 19. Flushing Operation

[0496] 20. Flush Function

[0497] 21. Stop-After-Picture

[0498] 22. Multi-Standard Search Mode

[0499] 23. Inverse Modeler

[0500] 24. inverse Quantizer

[0501] 25. Huffman Decoder and Parser

[0502] 26. Diverse Discrete Cosine Transformer

[0503] 27. Buffer Manager

[0504] 1. Multi-standard Configurations

[0505] Since the various compression standards, i.e., JPEG, PPEG andH.261, are well known, as for example as described in the aforementionedU.S. Pat. No. 5,212,742, the detailed specifications of those standardsare not repeated here.

[0506] As previously mentioned, the present invention is capable ofdecompressing a variety of differently encoded, picture data bitstreams.In each of the different standards of encoding, some form of outputformatter is required to take the data presented at the output of thespatial decoder operating alone, or the serial output of a spatialdecoder and temporal decoder operating in combination, (as subsequentlydescribed herein in greater detail) and reformatting this output foruse, including display in a computer or other display systems, includinga video display system. Implementation of this formatting variessignificantly between encoding standards and/or the type of displayselected.

[0507] In a first embodiment, in accordance with the present invention,as previously described with reference to FIGS. 10-12 an addressgenerator is employed to store a block of formatted data, output fromeither the first decoder (Spatial Decoder) or the combination of thefirst decoder (Spatial Decoder) and the second decoder (the TemporalDecoder), and to write the decoded information into and/or from a memoryin a raster order. The video formatter described hereinafter provides awide range of output signal combinations.

[0508] In the preferred multi-standard video decoder embodiment of thepresent invention, the Spatial Decoder and the Temporal Decoder arerequired to implement both an MPEG encoded signal and an H.261 videodecoding system. The DRAM interfaces on both devices are configurable toallow the quantity of DRAM required to be reduced when working withsmall picture formats and at low coded data rates. The reconfigurationof these DRAMs will be further described hereinafter with reference tothe DRAM interface. Typically, a single 4 megabyte DRAM is required byeach of the Temporal Decoder and the Spatial Decoder circuits.

[0509] The Spatial Decoder of the present invention performs all therequired processing within a single picture. This reduces the redundancywithin one picture.

[0510] The Temporal Decoder reduces the redundancy between the subjectpicture with relationship to a picture which arrives prior to thearrival of the subject picture, as well as a picture which arrives afterthe arrival of the subject picture. One aspect of the Temporal Decoderis to provide an address decode network which handles the complexaddressing needs to read out the data associated with all of thesepictures with the least number of circuits and with high speed andimproved accuracy.

[0511] As previously described with reference to FIG. 11, the dataarrives through the Start Code Detector, a FIFO register which precedesa Huffman decoder and parser, through a second FIFO register, an inversemodeller, an inverse quantizer, inverse zigzag and inverse DCT. The twoFIFOs need not be on the chip. In one embodiment, the data does not flowthrough a FIFO that is on the chip. The data is applied to the DRAMinterface, and the FIFO-IN storage register and the FIFO-OUT register isoff the chip in both cases. These registers, whose operation is entirelyindependent of the standards, will subsequently be described herein infurther detail.

[0512] The majority of the subsystems and stages shown in FIG. 11 areactually independent of the particular standard used and include theDRAM interface 58, the buffer manager 59 which is generating addressesfor the DRAM interface, the inverse modeller 75, the inverse zig-zag 81and the inverse DCT 83. The standard independent units within theHuffman decoder and parser include the ALU 66 and the token formatter71.

[0513] Referring now to FIG. 12, the standard-independent units includethe DRAM interface 100, the fork 91, the FIFO register 96, the summer 98and the output selector 106. The standard dependent units are theaddress generator 94, which is different in H.261 and in MPEG, and theprediction filter 103, which is reconfiigurable to have the ability todo both H.261 and MPEG. The JPEG data will flow through the entiremachine completely unaltered.

[0514]FIG. 13 depicts a high level block diagram of the video formatterchip. The vast majority of this chipis independent of the standard. Theonly items that are affected by the standard is the way the data iswritten into the DRAM in the case of H.261, which differs from MPEG orJPEG; and that in H.261, it is not necessary to code every singlepicture. There is some timing information referred to as a temporalreference which provides some information regarding when the picturesare intended to be displayed, and that is also handled by the addressgeneration type of logic in the video formatter.

[0515] The remainder of the circuitry embodied in the video formatter,including all of the color space conversion, the up-sampling filters andall of the gamma correction RAMs, is entirely independent of theparticular compression standard utilized.

[0516] The Start Code Detector of the present invention is dependent onthe compression standard in that it has to recognize different startcode patterns in the bitstream for each of the standards. For example,H.261 has a 16 bit start code, MPEG has a 24 bit start code and JPEGuses marker codes which are fairly different from the other start codes.Once the Start Code Detector has recognized those different start codes,its operation is essentially independent of the compression standard.For instance, during searching, apart from the circuitry that recognizesthe different category of markers, much of the operation is very similarbetween the three different compression standards.

[0517] The next unit is the state machine 68 (FIG. 11) located withinthe Huffman decoder and parser. Here, the actual circuitry is almostidentical for each of the three compression standards. In fact, the onlyelement that is affected by the standard in operation is the resetaddress of the machine. If just the parser is reset, then it jumps to adifferent address for each standard. There are, in fact, four standardsthat are recognized. These standards are H.261, JPEG, MPEG and oneother, where the parser enters a piece of code that is used for testing.This illustrates that the circuitry is identical in almost every aspect,but the difference is the program in the microcode for each of thestandards. Thus, when operating in H.261, one program is running, andwhen a different program is running, there is no overlap between them.The same holds true for JPEG, which is a third, completely independentprogram.

[0518] The next unit is the Huffman decoder 56 which functions with theindex to data unit 64. Those two units cooperate together to perform theHuffman decoding. Here, the algorithm that is used for Huffman decodingis the same, irrespective of the compression standard. The changes arein which tables are used and whether or not the data coming into theHuffman decoder is inverted. Also, the Huffman decoder itself includes astate machine that understands some aspects of the coding standards.These different operations are selected in response to an instructioncoming from the parser state machine. The parser state machine operateswith a different program for each of the three compression standards andissues the correct command to the Huffman decoder at different timesconsistent with the standard in operation.

[0519] The last unit on the chip that is dependent on the compressionstandard is the inverse quantizer 79, where the mathematics that theinverse quantizer performs are different for each of the differentstandards. In this regard, a CODINGSTANDARD token is decoded and theinverse quantizer 79 remembers which standard it is operating in. Then,any subsequent DATA tokens that happen after that event, but beforeanother CODING_STANDARD may come along, are dealt with in the wayindicated by the CODING_STANDARD that has been remembered inside theinverse quantizer. In the detailed description, there is a tableillustrating different parameters in the different standards and whatcircuitry is responding to those different parameters or mathematics.

[0520] The address generation, with reference to H.261, differs for eachof the subsystems shown in FIG. 12 and FIG. 13. The address generationin FIG. 11, which generates addresses for the two FIFOs before and afterthe Hufffman decoder, does not change depending on the coding standards.Even in H.261, the address generation that happens on that chip isunaltered. Essentially, the difference between these standards is thatin MPEG and JPEG, there is an organization of macroblocks that are inlinear lines going horizontally across pictures. As best observed inFIG. 14a, a first macroblock A covers one full line. A macroblock Bcovers less than a line. A macroblock C covers multiple lines. Thedivision in MPEG is into slices 132, and a slice may be one horizontalline, A, or it may be part of a horizontal line B, or it may extend fromone-line into the next line, C. Each of these slices 132 is made up of arow of macroblocks.

[0521] In H.261, the organization is rather different because thepicture is divided into groups of blocks (GOB). A group of blocks isthree rows of macroblocks high by eleven macroblocks wide. In the caseof a CIF picture, there are twelve such groups of blocks. However, theyare not organized one above the other. Rather, there are two groups ofblocks next to each other and then six high, i.e., there are 6 GOB'svertically, and 2 GOB's horizontally.

[0522] In all other standards, when performing the addressing, themacroblocks are addressed in order as described above. Morespecifically, addressing proceeds along the lines and at the end of theline, the next line is started. In H.261, the order of the blocks is thesame as described within a group of blocks, but in moving onto the nextgroup of blocks, it is almost a zig-zag.

[0523] The present invention provides circuitry to deal with the latteraffect. That is the way in which the address generation in the spatialdecoder and the video formatter varies for H.261. This is accomplishedwhenever information is written into the DRAM. It is written with theknowledge of the aforementioned address generation sequence so the placewhere it is physically located in the RAM is exactly the same as if thishad been an MPEG picture of the same size. Hence, all of the addressgeneration circuitry for reading from the DRAM, for instance, whenforming predictions, does not have to comprehend that it is H.261standard because the physical placement of the information in the memoryis the same as it would have been if it had been in MPEG sequence. Thus,in all cases, only writing of data is affected.

[0524] In the Temporal Decoder, there is an abstraction for H.261 wherethe circuitry pretends something is different from what is actuallyoccurring. That is, each group of blocks is conceptually stretched outso that instead of having a rectangle which is 11×3 macroblocks, themacroblocks are stretched out into a length of 33 blocks (see FIG. 14c)group of blocks which is one macroblock high. By doing that, exactly thesame counting mechanisms used on the Temporal Decoder for countingthrough the groups of blocks are also used for MPEG.

[0525] There is a correspondence in the way that the circuitry isdesigned between an H.261 group of blocks and an MPEG slice. When H.261data is processed after the Start Code Detector, each group of blocks ispreceded by a slicestartcode. The next group of blocks is preceded bythe next slicestart code. The counting that goes on inside the TemporalDecoder for counting through this structure pretends that it is a 33macroblock-long group that is one macroblock high. This is sufficient,although the circuitry also counts every 11th interval. When it countsto the 11th macroblock or the 22nd macroblock, it resets some counters.This is accomplished by simple circuitry with another counter thatcounts up each macroblock, and when it gets to 11, it resets to zero.The microcode interrogates that and does that work. All the circuitry inthe temporal decoder of the present invention is essentially independentof the compression standard with respect to the physical placement ofthe macroblocks.

[0526] In terms of multi-standard adaptability, there are a number ofdifferent tables and the circuitry selects the appropriate table for theappropriate standard at the appropriate time. Each standard has multipletables; the circuitry selects from the set at any given time. Within anyone standard, the circuitry selects one table at one time and anothertable another time. In a different standard, the circuitry selects adifferent set of tables. There is some intersection between those tablesas indicated previously in the discussion of FIG. 15. For example, oneof the tables used in MPEG is also used in JPEG. The tables are not acompletely isolated set. FIG. 15 illustrates an H.261 set, an MPEG setand a JPEG set. Note that there is a much greater overlap between theH.261 set and the MPEG set. They are quite common in the tables theyutilize. There is a small overlap between MPEG and JPEG, and there is nooverlap at all between H.261 and JPEG so that these standards havetotally different sets of tables.

[0527] As previously indicated, most of the system units are compressionstandard independent. If a unit is standard independent, and such unitsneed not remember what CODING_STANDARD is being processed. All of theunits that are standard dependent remember the compression standard asthe CODING_STANDARD token flows by them. When informationencoded/decoded in a first coding standard is distributed through themachine, and a machine is changing standards, prior machines undermicroprocessor control would normally choose to perform in accordancewith the H.261 compression standard. The MPU in such prior machinesgenerates signals stating in multiple different places within themachine that the compression standard is changing. The MPU makes changesat different times and, in addition, may flush the pipeline through.

[0528] In accordance with the invention, by issuing a change ofCODING_STANDARD tokens at the Start Code Detector that is positioned asthe first unit in the pipeline, this change of compression standard isreadily handled. The token says a certain coding standard is beginningand that control information flows down the machine and configures allthe other registers at the appropriate time. The MPU need not programeach register.

[0529] The prediction token signals how to form predictions using thebits in the bitstream. Depending on which compression standard isoperating, the circuitry translates the information that is found in thestandard, i.e. from the bitstream into a prediction mode token. Thisprocessing is performed by the Huffman decoder and parser state machine,where it is easy to manipulate bits based on certain conditions. TheStart Code Detector generates this prediction mode token. The token thenflows down the machine to the circuitry of the Temporal Decoder, whichas the device responsible for forming predictions. The circuitry of thespatial decoder interprets the token without having to know whatstandard it is operating in because the bits in it are invariant in thethree different standards. The Spatial Decoder just does what it is toldin response to that token. By having these tokens and using themappropriately, the design of other units in the machine is simplified.Although there may be some complications in the program, benefits arereceived in that some of the hard wired logic which would be difficultto design for multi-standards can be used here.

[0530] 2. JPEG Still Picture Decoding

[0531] As previously indicated, the present invention relates to signaldecompression and, more particularly, to the decompression of an encodedvideo signal, irrespective of the compression standard employed.

[0532] One aspect of the present invention is to provide a first decodercircuit (the Spatial Decoder) to decode a first encoded signal (the JPEGencoded video signal) in combination with a second decoder circuit (theTemporal Decoder) to decode a first encoded signal (the MPEG or H.261encoded video signal) in a pipeline processing system. The TemporalDecoder is not needed for JPEG decoding.

[0533] In this regard, the invention facilitates the decompression of aplurality of differently encoded signals through the use of a singlepipeline decoder and decompression system. The decoding anddecompression pipeline processor is organized on a unique and specialconfiguration which allows the handling of the multi-standard encodedvideo signals through the use of techniques all compatible with thesingle pipeline decoder and processing system. The Spatial Decoder iscombined with the Temporal Decoder, and the Video Formatter is used indriving a video display.

[0534] Another aspect of the invention is the use of the combination ofthe Spatial Decoder and the Video Formatter for use with only stillpictures. The compression standard independent Spatial Decoder performsall of the data I processing within the boundaries of a single picture.Such a decoder handles the spatial decompression of the internal picturedata which is passing through the pipeline and is distributed withinassociated random access memories, standard independent addressgeneration circuits for handling the storage and retrieval ofinformation into the memories. Still picture data is decoded at theoutput of the Spatial Decoder, and this output is employed as input tothe multi-standard, configurable Video Formatter, which then provides anoutput to the display terminal. In a first sequence of similar pictures,each decompressed picture at the output of the Spatial Decoder is of thesame length in bits by the time the picture reaches the output of theSpatial Decoder. A second sequence of pictures may have a totallydifferent picture size and, hence, have a different length when comparedto the first length. Again, all such second sequence of similar picturesare of the same length in bits by the time such pictures reach theoutput of the Spatial Decoder.

[0535] Another aspect of the invention is to internally organize theincoming standard dependent bitstream into a sequence of control tokensand DATA tokens, in combination with a plurality ofsequentially-positioned reconfigurable processing stages selected andorganized to act as a standard-independent,reconfigurable-pipeline-processor.

[0536] With regard to JPEG decoding, a single Spatial Decoder with nooff chip DRAM can rapidly decode baseline JPEG images. The SpatialDecoder supports all features of baseline JPEG encoding standards.However, the image size that can be decoded may be limited by the sizeof the output buffer provided. The Spatial Decoder circuit also includesa random access memory circuit, having machine-dependent, standardindependent address generation circuits for handling the storage ofinformation into the memories.

[0537] As previously, indicated the Temporal Decoder is not required todecode JPEG-encoded video. Accordingly, signals carried by DATA tokenspass directly through the Temporal Decoder without further processingwhen the Temporal Decoder is configured for a JPEG operation.

[0538] Another aspect of the present invention is to provide in theSpatial Decoder a pair of memory circuits, such as buffer memorycircuits, for operating in combination with the Huffman decoder/videodemultiplexor circuit (HD & VDM). A first buffer memory is positionedbefore the HD & VDM, and a second buffer memory is positioned after theHD & VDM. The HD & VDM decodes the bitstream from the binary ones andzeros that are in the standard encoded bitstream and turns such streaminto numbers that are used downstream. The advantage of the two buffersystem is for implementing a multi-standard decompression system. Thesetwo buffers, in combination with the identified implementation of theHuffman decoder, are described hereinafter in greater detail.

[0539] A still further aspect of the present multi-standard,decompression circuit is the combination of a Start Code Detectorcircuit positioned upstream of the first forward buffer operating incombination with the Huffman decoder. One advantage of this combinationis increased flexibility in dealing with the input bitstream,particularly padding, which has to be added to the bitstream. Theplacement of these identified components, Start Code Detector, memorybuffers, and Huffman decoder enhances the handling of certain sequencesin the input bitstream.

[0540] In addition, off chip DRAMs are used for decoding JPEG-encodedvideo pictures in real time. The size and speed of the buffers used withthe DRAMs will depend on the video encoded data rates.

[0541] The coding standards identify all of the standard dependent typesof information that is necessary for storage o in the DRAMs associatedwith the Spatial Decoder using standard independent circuitry.

[0542] 3. Motion Picture Decompression

[0543] In the present invention, if motion pictures are beingdecompressed through the steps of decoding, a further Temporal Decoderis necessary. The Temporal Decoder combines the data decoded in theSpatial Decoder with pictures, previously decoded, that are intended fordisplay either before or after the picture being currently decoded. TheTemporal Decoder receives, in the picture coded datastream, informationto identify this temporally-displaced information. The Temporal Decoderis organized to address temporally and spatially displaced information,retrieve it, and combine it in such a way as to decode the informationlocated in one picture with the picture currently being decoded andending with a resultant picture that is complete and is suitable fortransmission to the video formatter for driving the display screen.Alternatively, the resultant picture can be stored for subsequent use intemporal decoding of subsequent pictures.

[0544] Generally, the Temporal Decoder performs the processing betweenpictures either earlier and/or later in time with reference to thepicture currently being decoded. The Temporal Decoder reintroducesinformation that is not encoded within the coded representation of thepicture, because it s redundant and is already available at the decoder.More specifically, it is probable that any given picture will containsimilar information as pictures temporally surrounding it, both beforeand after. This similarity can be made greater if motion compensation isapplied. The Temporal Decoder and decompression circuit also reduces theredundancy between related pictures.

[0545] In another aspect of the present invention, the Temporal Decoderis employed for handling the standard-dependent output information fromthe Spatial Decoder. This standard dependent information for a singlepicture is distributed among several areas of DRAM in the sense that thedecompressed output information, processed by the Spatial Decoder, isstored in other DRAM registers by other random access memories havingstill other machine-dependent, standard-independent address generationcircuits for combining one picture of spatially decoded informationpacket of spatially decoded picture information, temporally displacedrelative to the temporal position of the first picture.

[0546] In multi-standard circuits capable of decoding MPEG-encodedsignals, larger logic DRAM buffers may be required to support the largerpicture formats possible with MPEG.

[0547] The picture information is moving through the serial pipeline in8 pel by 8 pel blocks. In one form of the invention, the addressdecoding circuitry handles these pel blocks (storing and retrieving)along such block boundaries. The address decoding circuitry also handlesthe storing and retrieving of such 8 by 8 pel blocks across suchboundaries. This versatility is more completely described hereinafter.

[0548] A second Temporal Decoder may also be provided which passes theoutput of the first decoder circuit (the Spatial Decoder) directly tothe Video Formatter for handling without signal processing delay.

[0549] The Temporal Decoder also reorders the blocks of picture data fordisplay by a display circuit. The address decode circuitry, describedhereinafter, provides handling of this reordering.

[0550] As previously mentioned, one important feature of the TemporalDecoder is to add picture information together from a selection ofpictures which have arrived earlier or later than the picture underprocessing. When a picture is described in this context, it may mean anyone of the following:

[0551] 1. The coded data representation of the picture;

[0552] 2. The result, i.e., the final decoded picture resulting from theaddition of a process step performed by the decoder;

[0553] 3. Previously decoded pictures read from the DRAM; and

[0554] 4. The result of the spatial decoding, i.e., the extent of databetween a PICTURE_START token and a subsequent PICTURE_END token.

[0555] After the picture data information is processed by the TemporalDecoder, it is either displayed or written back into a picture memorylocation. This information is then kept for further reference to be usedin processing another different coded data picture.

[0556] Re-ordering of the MPEG encoded pictures for visual displayinvolves the possibility that a desired scrambled picture can beachieved by varying the re-ordering feature of the Temporal Decoder.

[0557] 4. RAM Memory Map

[0558] The Spatial Decoder, Temporal Decoder and Video Formatter all useexternal DRAM. Preferably, the same DRAM is used for all three devices.While all three devices use DRAM, and all three devices use a DRAMinterface in conjunction with an address generator, what each implementsin DRAM is different. That is, each chip, e.g. spatial Decoder andTemporal Decoder, have a different DRAM interface and address generationcircuitry even through they use a similar physical, external DRAM.

[0559] In brief, the Spatial Decoder implements two FIFOs in the commonDRAM. Referring again to FIG. 11, one FIFO 54 is positioned before theHuffman decoder 56 and parser, and the other is positioned after theHuffman decoder and parser. The FIFOs are implemented in a relativelystraightforward manner. For each FIFO, a particular portion of DRAM isset aside as the physical memory in which the FIFO will be implemented.

[0560] The address generator associated with the Spatial Decoder DRAMinterface 58 keeps track of FIFO addresses using two pointers. Onepointer points to the first word stored in the FIFO, the other pointerpoints to the last word stored in the FIFO, thus allowing read/writeoperation on the appropriate word. When, in the course of a read orwrite operation, the end of the physical memory is reached, the addressgenerator “wraps around” to the start of the physical memory.

[0561] In brief, the Temporal Decoder of the present invention must beable to store two full pictures or frames of whatever encoding standard(MPEG or H.261) is specified. For simplicity, the physical memory in theDRAM into which the two frames are stored is split into two halves, witheach half being dedicated (using appropriate pointers) to a particularone of the two pictures.

[0562] MPEG uses three different picture types: Intra (I) Predicted (P)and Bidirectionally interpolated (B). As previously mentioned, Bpictures are based on predictions from two pictures. One picture is fromthe future and one from the past. I pictures require no further decodingby the Temporal Decoder, but must be stored in one of the two picturebuffers for later use in decoding P and B pictures. Decoding P picturesrequires forming predictions from a previously decoded P or I picture.The decoded P picture is stored in a picture buffer for use decoding Pand B pictures. B pictures can require predictions form both of thepicture buffers. However, B pictures are not stored in the externalDRAM.

[0563] Note that I and P pictures are not output from the TemporalDecoder as they are decoded. Instead, I and P pictures are written intoone of the picture buffers, and are read out only when a subsequent I orP picture arrives for decoding. In other words, the Temporal Decoderrelies on subsequent P or I pictures to flush previous pictures out ofthe two picture buffers, as further discussed hereinafter in the sectionon flushing. In brief, the Spatial Decoder can provide a fake I or Ppicture at the end of a video sequence to flush out the last P or Ipicture. In turn, this fake picture is flushed when a subsequent videosequence starts.

[0564] The peak memory band width load occurs when decoding B pictures.The worst case is the B frame may be formed from predictions from boththe picture buffers, with all predictions being made to half-pixelaccuracy.

[0565] As previously described, the Temporal Decoder can be configuredto provide MPEG picture reordering. With this as picture reordering, theoutput of P and I pictures is delayed until the next P or I picture inthe data stream starts to be decoded by the Temporal Decoder.

[0566] As the P or I pictures are reordered, certain tokens are storedtemporarily on chip as the picture is written into the picture buffers.When the picture is read out for display, these stored tokens areretrieved. At the output of the Temporal Decoder, the DATA Tokens of thenewly decoded P or I picture are replaced with DATA Tokens for the olderP or picture.

[0567] In contrast, H.261 makes predictions only from the picture justdecoded. As each picture is decoded, it is written into one of the twopicture buffers so it can be used in decoding the next picture. The onlyDRAM memory operations required are writing 8×8 blocks, and formingpredictions with integer accuracy motion vectors.

[0568] In brief, the Video Formatter stores three frames or pictures.Three pictures need to be stored to accommodate such features asrepeating or skipping pictures.

[0569] 5. Bitstream Characteristics

[0570] Referring now particularly to the Spatial Decoder of the presentinvention, it is helpful to review the bitstream characteristics of theencoded datastream as these characteristics must be handled by thecircuitry of the Spatial Decoder and the Temporal Decoder. For example,under one or more compression standards, the compression ratio of thestandard is achieved by varying the number of bits that it uses to codethe pictures of a picture. The number of bits can vary by a wide margin.Specifically, this means that the length of a bitstream used to encode areferenced picture of a picture might be identified as being one unitlong, another picture might be a number of units long, while still athird picture could be a fraction of that unit.

[0571] None of the existing standards (MPEG 1.2, JPEG, H.261) define away of ending a picture, the implication being that when the nextpicture starts, the current one has finished.

[0572] Additionally, the standards (H.261 specifically) allow incompletepictures to be generated by the encoder.

[0573] In accordance with the present invention, there is provided a wayof indicating the end of a picture by using one of its tokens:PICTURE_END. The still encoded picture data leaving the Start CodeDetector consists of pictures starting with a PICTURE_START token andending with a PICTURE_END token, but still of widely varying length.There may be other information transmitted here (between the first andsecond picture), but it is known that the first picture has finished.

[0574] The data stream at the output of the Spatial Decoder consists ofpictures, still with picture-starts and picture-ends, of the same length(number of bits) for a given sequence. The length of time between apicture-start and a picture-end may vary.

[0575] The Video Formatter takes these pictures of non-uniform time anddisplays them on a screen at a fixed picture rate determined by the typeof display being driven. Different display rates are used throughout theworld, e.g. PAL-NTSC television standards. This is accomplished byselectively dropping or repeating pictures in a manner which is unique.Ordinary “frame rate converters,” e.g. 2-3 pulldown, operate with afixed input picture rate, whereas the Video Formatter can handle avariable input picture rate.

[0576] 6. Reconpigurable Processing Stage

[0577] Referring again to FIG. 10, the reconfigurable processing stage(RPS) comprises a token decode circuit 33 which is employed to receivethe tokens coming from a two wire interface 37 and input latches 34. Theoutput of the token decode circuit 33 is applied to a processing unit 36over the two-wire interface 37 and an action identification circuit 39.The processing unit 36 is suitable for processing data under the controlof the action identification circuit 39. After the processing iscompleted, the processing unit 36 connects such completed signals to theoutput, two-wire interface bus 40 through output latches 41.

[0578] The action identification decode circuit 39 has an input from thetoken decode circuit 33 over the two-wire interface bus 40 and/or frommemory circuits 43 and 44 over two-wire interface bus 46. The tokensfrom the token decode circuit 33 are applied simultaneously to theaction identification circuit 39 and the processing unit 36. The actionidentification function as well as the RPS is described in furtherdetail by tables and figures in a subsequent portion of thisspecification.

[0579] The functional block diagram in FIG. 10 illustrates those stagesshown in FIGS. 11, 12 and 13 which are not standard independentcircuits. The data flows through the token decode circuit 33, throughthe processing unit 36 and onto the two-wire interface circuit 42through the output latches 41. If the Control Token is recognized by theRPS, it is decoded in the token decode circuit 33 and appropriate actionwill be taken. If it is not recognized, it will be passed unchanged tothe output two-wire interface 42 through the output circuit 41. Thepresent invention operates as a pipeline processor having a two-wireinterface for controlling the movement of control tokens'through thepipeline. This feature of the invention is described in greater detailin the previously filed EPO patent application number 92306038.8.

[0580] In the present invention, the token decode circuit 33 is employedfor identifying whether the token presently entering through thetwo-wire interface 42 is a DATA token or control token. In the eventthat the token being examined by the token decode circuit 33 isrecognized, it is exited to the action identification circuit 39 with aproper index signal or flag signal indicating that action is to betaken. At the same time, the token decode circuit 33 provides a properflag or index signal to the processing unit 36 to alert it to thepresence of the token being handled by the action identification circuit39.

[0581] Control Tokens may also be Processed.

[0582] A more detailed description of the various types of tokens usablein the present invention will be subsequently described hereinafter. Forthe purpose of this portion of the specification, it is sufficient tonote that the address carried by the control token is decoded in thedecoder 33 and is used to access registers contained within the actionidentification circuit 39. When the token being examined is a recognizedcontrol token, the action identification circuit 39 uses itsreconfiguration state circuit for distributing the control signalsthroughout the state machine. As previously mentioned, this activatesthe state machine of the action identification decoder 39, which thenreconfigures itself. For example, it may change coding standards. Inthis way, the action identification circuit 39 decodes the requiredaction for handling the particular standard now passing through thestate machine shown with reference to FIG. 10.

[0583] Similarly, the processing unit 36 which is under the control ofthe action identification circuit 39 is now ready to process theinformation contained in the data fields of the DATA token when it isappropriate for this to occur. On many occasions, a control tokenarrives first, reconfigures the action identification circuit 39 and isimmediately followed by a DATA token which is then processed by theprocessing unit 36. The control token exits the output latches circuit41 over the output two-wire interface 42 immediately preceding the DATAtoken which has been processed within the processing unit 36.

[0584] In the present invention, the action identification circuit, 39,is a state machine holding history state. The registers, 43 and 44 holdinformation that has been decoded from the token decoder 33 and storedin these registers. Such registers can be either on-chip or-off chip asneeded. These plurality of state registers contain action informationconnected to the action identification currently being identified in theaction identification circuit 39. This action information has beenstored from previously decoded tokens and can affect the action that isselected. The connection 40 is going straight from the token decode 33to the action identification block 39. This is intended to show that theaction can also be affected by the token that is currently beingprocessed by the token decode circuit 33.

[0585] In general, there is shown token decoding and data processing inaccordance with the present invention. The data processing is performedas configured by the action identification circuit 39. The action isaffected by a number of conditions and is affected by informationgenerally derived from a previously decoded token or, more specifically,information stored from previously decoded tokens in registers 43 and44, the current token under processing, and the state and historyinformation that the action identification unit 39 has itself acquired.A distinction is thereby shown between Control tokens and DATA tokens.

[0586] In any RPS, some tokens are viewed by that RPS unit as beingControl tokens in that they affect the operation of the RPS presumablyat some subsequent time. Another set of tokens are viewed by the RPS asDATA tokens. Such DATA tokens contain information which is processed bythe RPS in a way that is determined by the design of the particularcircuitry, the tokens that have been previously decoded and the state ofthe action identification circuit 39. Although a particular RPSidentifies a certain set of tokens for that particular RPS control andanother set of tokens as data, that is the view of that particular RPS.Another RPS can have a different view of the same token. Some of thetokens might be viewed by one RPS unit as DATA Tokens while another RPSunit might decide that it is actually a Control Token, For example, thequantization table information, as far as the Huffmran decoder and statemachine is concerned, is data, because it arrives on its input as codeddata, it gets formatted up into a series of 8 bit words, and they getformed into a token called a quantization table token (QUANT_TABLE)which goes down the processing pipeline. As far as that machine isconcerned, all of that was data; it was handling data, transforming onesort of data into another sort of data, which is clearly a function ofthe processing performed by that portion of the machine. However, whenthat information gets to the inverse quantizer, it stores theinformation in that token a plurality of registers. In fact, becausethere are 64 8-bit numbers and there are many registers, in general,many registers may be present. This information is viewed as controlinformation, and then that control information affects the processingthat is done on subsequent DATA tokens because it affects the numberthat you multiply each data word. There is an example where one stageviewed that token as being data and another stage viewed it as beingcontrol.

[0587] Token data, in accordance with the invention is almostuniversally viewed as being data through the machine. One of theimportant aspects is that, in general, each stage of circuitry that hasa token decoder will be looking for a certain set of tokens, and anytokens that it does not recognize will be passed unaltered through thestage and down the pipeline, so that subsequent stages downstream of thecurrent stage have the benefit of seeing those tokens and may respond tothem. This is an important feature, namely there can be communicationbetween blocks that are not adjacent to one another using the tokenmechanism.

[0588] Another important feature of the invention is that each of thestages of circuitry has the processing capability within it to be ableto perform the necessary operations for each of the standards, and thecontrol, as to which operations are to be performed at a given time,come as tokens. There is one processing element that differs between thedifferent stages to provide this capability. In the state machine ROM ofthe parser, there are three separate entirely different programs, onefor each of the standards that are dealt with. Which program is executeddepends upon a CODING_STANDARD token. In otherwords, each of these threeprograms has within it the ability to handle both decoding and theCODING STANDARD standard token. When each of these programs sees whichcoding standard, is to be decoded next, they literally jump to the startaddress in the microcode ROM for that particular program. This is howstages deal with multi-standardness.

[0589] Two things are affected by the different standards. First, itaffects what pattern of bits in the bitstream are recognized as astart-code or a marker code in order to reconfigure the shift registerto detect the length of the start marker code. Second, there is a pieceof information in the microcode that denotes what that start or markercode means. Recall that the coding of bits differs between the threestandards. Accordingly, the microcode looks up in a table, specific tothat compressor standard, something that is independent of the standard,i.e., a type of token that represents the incoming codes. This token istypically independent of the standard since in most cases, each of thevarious standards provide a certain code that will produce it.

[0590] The inverse quantizer 79 has a mathematical capability. Thequantizer multiplies and adds, and has the ability to do all threecompression standards which are configured by parameters. For example, aflag bit in the ROM in control tells the inverse quantizer whether ornot to add a constant, K. Another flag tells the inverse quantizerwhether to add another constant. The inverse quantizer remembers in aregister the CODING_STANDARD token as it flows by the guantizer. WhenDATA tokens pass thereafter, the inverse guantizer remembers what thestandard is and it looks up the parameters that it needs to apply to theprocessing elements in order to perform a proper operation. For example,the inverse quantizer will look up whether K is set to 0, or whether itis set to 1 for a particular compression standard, and will apply thatto its processing circuitry.

[0591] In a similar sense the Huffman decoder 56 has a number of tableswithin it, some for JPEG, some for MPEG and some for H.261. The majorityof those tables, in fact, will service more than one of thosecompression standards. Which tables are used depends on the syntax ofthe standard. The Huffman decoder works by receiving a command from thestate machine which tells it which of the tables to use. Accordingly,the Huffman decoder does not itself directly have a piece of state goinginto it, which is remembered and which says what coding it isperforming. Rather, it is the combination of the parser state machineand Huffman decoder together that contain information within them.

[0592] Regarding the Spatial Decoder of the present invention, theaddress generation is modified and is similar to that shown in FIG. 10,in that a number of pieces of information are decoded from tokens, suchas the coding standard. The coding standard and additional informationas well, is recorded in the registers and that affects the progress ofthe address generator state machine as it steps through and counts themacroblocks in the system, one after the other. The last stage would bethe prediction filter 179 (FIG. 17) which operates in one of two modes,either H.261 or MPEG and are easily identified.

[0593] 7. Multi-standard Coding

[0594] The system of the present invention also provides a combinationof the standard-independent indices generation circuits, which arestrategically placed throughout the system in combination with the tokendecode circuits. For example, the system is employed for specificallydecoding either the H.261 video standard, or the MPEG video standard orthe JPEG video standard. These three compression coding standardsspecify similar processes to be done on the arriving data, but thestructure of the datastreams is different. As previously discussed, itis one of the functions of the Start Code Detector to detect MPEGstart-codes, H.261 start-codes, and JPEG marker codes, and convert themall into a form, i.e., a control token which includes a token streamembodying the current coding standard. The control tokens are passedthrough the pipeline processor, and are used, i.e., decoded, in thestate machines to which they are relevant, and are passed through otherstate machines to which the tokens are not relevant. In this regard, theDATA Tokens are treated in the same fashion, insofar as they areprocessed only in the state machines that are configurable by thecontrol tokens into processing such DATA Tokens. In the remaining statemachines, they pass through unchanged.

[0595] More specifically, a control token in accordance with the presentinvention, can consist of more than one word in the token. In that case,a bit known as the extension bit is set specifying the use of additionalwords in the token for carrying additional information. Certain of theseadditional control bits contain indices indicating information for usein corresponding state machines to create a set of standard-independentindices signals. The remaining portions of the taken are used toindicate and identify the internal processing control function which isstandard for all of the datastreams passing through the pipelineprocessor. In one form of the invention, the token extension is used tocarry the current coding standard which is decoded by the relative tokendecode circuits distributed throughout the machine, and is used toreconfigure the action identification circuit 39 of stages throughoutthe machine wherever it is appropriate to operate under a new codingstandard. Additionally, the token decode circuit can indicate whether acontrol token is related to one of the selected standards which thecircuit was designed to handle.

[0596] More specifically, an MPEG start code and a JPEG marker arefollowed by an 8 bit value. The H.261 start code is followed by a 4 bitvalue. In this context, the Start Code Detector 51, by detecting eitheran MPEG start-code or a JPEG marker, indicates that the following 8 bitscontain the value associated with the start-code. Independently, it canthen create a signal which indicates that it is either an MPEG startcode or a JPEG marker and not an H.261 start code. In this firstinstance, the 8 bit value is entered into a decode circuit, part ofwhich creates a signal indicating the index and flag which is usedwithin the current circuit for handling the tokens passing through thecircuit. This is also used to insert portions of the control token whichwill be looked at thereafter to determine which standard is beinghandled. In this sense, the control token contains a portion indicatingthat it is related to an MPEG standard, as well as a portion whichindicates what type of operation should be performed on the accompanyingdata. As previously discussed, this information is utilized in thesystem to reconfigure the processing stage used to perform the functionrequired by the various standards created for that purpose.

[0597] For example, with reference to the H.261 start code, it isassociated with a 4 bit value which follows immediately after the startcode. The Start Code Detector passes this value into the token generatorstate machine. The value is applied to an 8 bit decoder which produces a3 bit start number. The start number is employed to identify thepicture-start of a picture number as indicated by the value.

[0598] The system also includes a multi-stage parallel processingpipeline operating under the principles of the two-wire interfacepreviously described. Each of the stages comprises a machine generallytaking the form illustrated in FIG. 10. The token decode circuit 33 isemployed to direct the token presently entering the state machine intothe action identification circuit 39 or the processing unit 36, asappropriate. The processing unit has been previously reconfigured by thenext previous control token into the form needed for handling thecurrent coding standard, which is now entering the processing stage andcarried by the next DATA token. Further, in accordance with this aspectof the invention, the succeeding state machines in the processingpipeline can be functioning under one coding standard, i.e., H.261,while a previous stage can be operating under a separate standard, suchas MPEG. The same two-wire interface is used for carrying both thecontrol tokens and the DATA Tokens.

[0599] The system of the present invention also utilizes control tokensrequired to decode a number of coding standards with a fixed number ofreconfigurable processing stages. More specifically, the PICTURE_ENDcontrol token is employed because it is important to have an indicationof when a picture actually ends. Accordingly, in designing amulti-standard machine, it is necessary to create additional controltokens within the multi-standard pipeline processing machine which willthen indicate which one of the standard decoding techniques to use. Sucha control token is the PICTURE_END token. This PICTURE_END token is usedto indicate that the current picture has finished, to force the buffersto be flushed, and to push the current picture through the decoder tothe display.

[0600] 8. Multi-standard Processing Circuit—Second Mode of Opertion

[0601] A compression standard-dependent circuit, in the form of thepreviously described Start Code Detector, is suitably interconnected toa compression standard-independent circuit over an appropriate bus. Thestandard-dependent circuit is connected to a combinationdependent-independent circuit over the same bus and an additional bus.The standard-independent circuit applies additional input to thestandard dependent-independent circuit, while the latter providesinformation back to the standard-independent circuit. Information fromthe standard-independent circuit is applied to the output over anothersuitable bus. Table 600 illustrates that the multiple standards appliedas the input to the standard-dependent Start Code Detector 51 includecertain bit streams which have standard-dependent meanings within eachencoded bit stream.

[0602] 9. Start-code Detector

[0603] As previously indicated the Start Code Detector, in accordancewith the present invention, is capable of taking MPEG, JPEG and H.261bit streams and generating from them a sequence of proprietary tokenswhich are meaningful to the rest of the decoder. As an example of howmulti-standard decoding is achieved, the MPEG (1 and 2)picture_start_code, the H.261 picture_start_code and the JPEGstart_of_scan (SOS) marker are treated as equivalent by the Start CodeDetector, and all will generate an internal PICTURE_START token. In asimilar way, the MPEG sequence_start_code and the JPEG SOI(start_of_image) marker both generate a machine sequence_start_token.The H.261 standard, however, has no equivalent start code. Accordingly,the Start Code Detector, in response to the first H.261picture_start_code, will generate a sequence_start token.

[0604] None of the above described images are directly used other thanin the SCD. Rather, a machine PICTURE_START token, for example, has beendeemed to be equivalent to the PICTURE_START images contained in the bitstream. Furthermore, it must be borne in mind that the machinePICTURE_START by itself, is not a direct image of the PICTURE_START inthe standard. Rather, it is a control token which is used in combinationwith other control tokens to provide standard-independent decoding whichemulates the operation of the images in each of the compression codingstandards. The combination of control tokens in combination with thereconfiguration of circuits, in accordance with the information carriedby control tokens, is unique in and of itself, as well as in furthercombination with indices and/or flags generated by the token decodecircuit portion of a respective state machine. A typical reconfigurablestate machine will be described subsequently.

[0605] Referring again to Table 600, there are shown the names of agroup of standard images in the left column. In the right column thereare shown the machine dependent control tokens used in the emulation ofthe standard encoded signal which is present or not used in the standardimage.

[0606] With reference to Table 600, it can be seen that a machinesequence_start signal is generated by the Start Code Detector, aspreviously described, when it decodes any one of the standard signalsindicated in Table 600. The Start Code Detector creates sequence_start,group_start, sequence_end, slice_start, user-data, extra-data andPICTURE_START tokens for application to the two-wire interface which isused throughout the system. Each of the stages which operate inconjunction with these control tokens are configured by the contents ofthe tokens, or are configured by indices created by contents of thetokens, and are prepared to handle data which is expected to be receivedwhen the picture DATA Token arrives at that station.

[0607] As previously described, one of the compression standards, suchas H.261, does not have a sequence_start image in its data stream, nordoes it have a PICTURE_END image in its data stream. The Start CodeDetector indicates the PICTURE_END point in the incoming bit stream andcreates a PICTURE_END token. In this regard, the system of the presentinvention is intended to carry data words that are fully packed tocontain a bit of information in each of the register positions selectedfor use in the practice of the present invention. To this end, 15 bitshave been selected as the number of bits which are passed between twostart codes. Of course, it will be appreciated by one of ordinary skillin the art, that a selection can be made to include either greater orfewer than 15 bits. In other words, all 15 bits of a data word beingpassed from the Start Code Detector into the DRAM interface are requiredfor proper operation. Accordingly, the Start Code Detector creates extrabits, called padding, which it inserts into the last word of a DATAToken. For purposes of illustration 15 data bits has been selected.

[0608] To perform the Padding operation, in accordance with the presentinvention, binary 0 followed by a number of binary 1's are automaticallyinserted to complete the 15 bit data word. This data is then passedthrough the coded data buffer and presented to the Huffman decoder,which removes the padding. Thus, an arbitrary number of bits can bepassed through a buffer of fixed size and width.

[0609] In one embodiment, a slice_start control token is used toidentify a slice of the picture. A slice_start control token is employedto segment the picture into smaller regions. The size of the region ischosen by the encoder, and the Start Code Detector identifies thisunique pattern of the slice_start code in order for themachine-dependent state stages, located downstream from the Start CodeDetector, to segment the picture being received into smaller regions.The size of the region is chosen by the encoder, recognized by the StartCode Detector and used by the recombination circuitry and control tokensto decompress the encoded picture. The slice_start_codes are principallyused for error recovery.

[0610] The start codes provide a unique method of starting up thedecoder, and this will subsequently be described in further detail.There are a number of advantages in placing the Start Code Detectorbefore the coded data buffer, as opposed to placing the Start CodeDetector after the coded data buffer and before the Huffman decoder andvideo demultiplexor. Locating the Start Code Detector before the firstbuffer allows it to 1) assemble the tokens, 2) decode the standardcontrol signals, such as start codes, 3) pad the bitstream before thedata goes into the buffer, and 4) create the proper sequence of controltokens to empty the buffers, pushing the available data from the buffersinto the Huffman Decoder.

[0611] Most of the control token output by the Start Code Detectordirectly reflect syntactic elements of the various picture and videocoding standards. The Start Code Detector converts the syntacticelements into control tokens. In addition to these natural tokens, someunique and/or machine-dependent tokens are generated. The unique tokensinclude those tokens which have been specifically designed for use withthe system of the present invention which are unique in and ofthemselves, and are employed for aiding in the multi-standard nature ofthe present invention. Examples of such unique tokens includePICTURE_END and CODING_STANDARD.

[0612] Tokens are also introduced to remove some of the syntacticdifferences between the coding standards and to function in co-operationwith the error conditions. The automatic token generation is done afterthe serial analysis of the standard-dependent data. Therefore, theSpatial Decoder responds equally to tokens that have been supplieddirectly to the input of the Spatial Decoder, i.e. the SCO, as well asto tokens that have been generated following the detection of thestart-codes in the coded data. A sequence of extra tokens is insertedinto the two-wire interface in order to control the multi-standardnature of the present invention.

[0613] The MPEG and H.261 coded video streams contain standarddependent, non-data, identifiable bit patterns, one of which ishereinafter called a start image and/or standard-dependent code. Asimilar function is served in JPEG, by marker codes. These start/markercodes identify significant parts of the syntax of the coded datastream.The analysis of start/marker codes performed by the Start Code Detectoris the first stage in parsing the coded data.

[0614] The start/marker code patterns are designed so that they can beidentified without decoding the entire bit stream. Thus, they can beused, in accordance with the present invention, to assist with errorrecovery and decoder start-up. The Start Code Detector providesfacilities to detect errors in the coded data construction and to assistthe start-up of the decoder. The error detection capability of the StartCode Detector will subsequently be discussed in further detail, as willthe process of starting up of the decoder.

[0615] The aforementioned description has been concerned primarilty withthe characteristics of the machine-dependent bit stream and itsrelationship with the addressing characteristics of the presentinvention. The following description is of the bit streamcharacteristics of the standard-dependent coded data with reference tothe Start Code Detector.

[0616] Each of the standard compression encoding systems employs aunique start code configuration or image which has been selected toidentify that particular compression specification. Each of the startcodes also carries with it a start code value. The start code value isemployed to identify within the language of the standard the type ofoperation that the start code is associated with. In the multi-standarddecoder of the present invention, the compatibility is based upon thecontrol token and DATA token configuration as previously described.Index signals, including flag signals, are circuit-generated within eachstate machine, and are described hereinafter as appropriate.

[0617] The start and/or marker codes contained in the standards, as wellas other standard words as opposed to data Words, are sometimesidentified as images to avoid confusion with the use of code and/ormachine-dependent codes to refer to the contents of control and/or DATAtokens used in the machine. Also, the term start code is often used as ageneric term to refer to JPEG marker codes as well as MPEG and H.261start codes. Marker codes and start codes serve the same purpose. Also,the term “flush” is used both to refer to the FLUSH token, and as averb, for example when referring to flushing the Start Code Detectorshift registers (including the signal “flushed”). To avoid confusion,the FLUSH token is always written in upper case. All other uses of theterm (verb or noun) are in lower case.

[0618] The standard-dependent coded input picture input stream comprisesdata and start images of varying lengths. The start images carry withthem a value telling the user what operation is to be performed on thedata which immediately follows according to the standard. However, inthe multi-standard pipeline processing system of the present invention,where compatibility is required for multiple standards, the system hasbeen optimized for handling all functions in all standards. Accordingly,in many situations, unique start control tokens must be created whichare compatible not only with the values contained in the values of theencoded signal standard image, but which are also capable of controllingthe various stages to emulate the operation of the standard asrepresented by specified parameters for each standard which are wellknown in the art. All such standards are incorporated by reference intothis specification.

[0619] It is important to understand the relationship between tokenswhich, alone or in combination with other control tokens, emulate thenondata information contained in the standard bit stream. A separate setof index signals, including flag signals, are generated by each statemachine to handle some of the processing within that state machine.Values carried in the standards can be used to access machine dependentcontrol signals to emulate the handling of the standard data andnon-data signals. For example, the slice_start token is a two wordtoken, and it is then entered onto the two wire interface as previouslydescribed.

[0620] The data input to the system of the present invention may be adata source from any suitable data source such as disk, tape, etc., thedata source providing 8 bit data to the first functional stage in theSpatial Decoder, the Start Code Detector 51 (FIG. 11). The Start CodeDetector includes three shift registers; the first shift register is 8bits wide, the next is 24 bits wide, and the next is 15 bits wide. Eachof the registers is part of the two-wire interface. The data from thedata source is loaded into the first register as a single 8 bit byteduring one timing cycle. Thereafter, the contents of the first shiftregister is shifted one bit at a time into the decode (second) shiftregister. After 24 cycles, the 24 bit register is full.

[0621] Every 8 cycles, the 8 bit bytes are loaded into the first shiftregister. Each byte is loaded into the value shift register 221 (FIG.20), and 8 additional cycles are used to empty it and load the shiftregister 231. Eight cycles are used to empty it, so after three of thoseoperations or 24 cycles, there are still three bytes in the 24 bitregister. The value decode shift register 230 is still empty.

[0622] Assuming that there is now a PICTURE_START word in the 24 bitshift register, the detect cycle recognizes the PICTURE_START codepattern and provides a start signal as its output. Once the detector hasdetected a start, the byte following it is the value associated withthat start code, and this is currently sitting in the value register221.

[0623] Since the contents of the detect shift register has beenidentified as a start code, its contents must be removed from the twowire interface to ensure that no further processing takes place usingthese 3 bytes. The decode register is emptied, and the value decodeshift register 230 waits for the value to be shifted all the way over tosuch register.

[0624] The contents now of the low order bit positions of the valuedecode shift register contains a value associated with thePICTURE_START. The Spatial Decoder equivalent to the standardPICTURE_START signal is referred to as the SD PICTURE_START signal. TheSD PICTURE_START signal itself is going to now be contained in the tokenheader, and the value is going to be contained in the extension word tothe token header.

[0625] 10. Tokens

[0626] In the practice of the present invention, a token is a universaladaptation unit in the form of an interactive interfacing messengerpackage for control and/or data functions and is adapted for use with areconfigurable processing stage (RPS) which is a stage, which inresponse to a recognized token, reconfigures itself to perform variousoperations.

[0627] Tokens may be either position dependent or position independentupon the processing stages for performance of various functions. Tokensmay also be metamorphic in that they can be altered by a processingstage and then passed down the pipeline for performance of furtherfunctions. Tokens may interact with all or less than all of the stagesand in this regard may interact with adjacent and/or non-adjacentstages. Tokens may be position dependent for some functions and positionindependent for other functions, and the specific interaction with astage may be conditioned by the previous processing history of a stage.

[0628] A PICTURE_END token is a way of signalling the end of a picturein a multi-standard decoder.

[0629] A multi-standard token is a way of mapping MPEG, JPEG and H.261data streams onto a single decoder using a mixture of standard dependentand standard independent hardware and IC control tokens.

[0630] A SEARCH_MODE token is a technique for searching MPEG, JPEG andH.261 data streams which allows random access and enhanced errorrecovery.

[0631] A STOP_AFTER_PICTURE token is a method of achieving a clear endto decoding which signals the end of a picture and clears the decoderpipeline, i.e., channel change.

[0632] Furthermore, padding a token is a way of passing an arbitrarynumber of bits through a fixed size, fixed width buffer.

[0633] The present invention is directed to a pipeline processing systemwhich has a variable configuration which uses tokens and a two-wiresystem. The use of control tokens and DATA Tokens in combination with atwo-wire system facilitates a multi-standard system capable of havingextended operating capabilities as compared with those systems which donot use control tokens.

[0634] The control tokens are generated by circuitry within the decoderprocessor and emulate the operation of a number of different typestandard-dependent signals passing into the serial pipeline processorfor handling. The technique used is to study all the parameters of themulti-standards that are selected for processing by the serial processorand noting 1) their similarities, 2) their dissimilarities, 3) theirneeds and requirements and 4) selecting the correct token function toeffectively process all of the standard signals sent into the serialprocessor. The functions of the tokens are to emulate the standards. Acontrol token function is used partially as an emulation/translationbetween the standard dependent signals and as an element to transmitcontrol information through the pipeline processor.

[0635] In prior art system, a dedicated machine is designed according towell-known techniques to identify the standard and then set up dedicatedcircuitry by way of microprocessor interfaces. Signals from themicroprocessor are used to control the flow of data through thededicated downstream components. The selection, timing and organizationof this decompression function is under the control of fixed logiccircuitry as assisted by signals coming from the microprocessor.

[0636] In contrast, the system of the present invention configures thedownstream functional stages under the control of the control tokens. Anoption is provided for obtaining needed and/or alternative control fromthe MPU.

[0637] The tokens provide and make a sensible format for communicatinginformation through the decompression circuit pipeline processor. In thedesign selected hereinafter and used in the preferred embodiment, eachword of a token is a minimum of 8 bits wide, and a single token canextend over one or fire words. The width of the token is changeable andcan be selected as any number of bits. An extension bit indicateswhether a token is extended beyond the current word, i.e., if it is setto binary one in all words of a token, except the last word of a token.If the first word of a token has an extension bit of zero, thisindicates that the token is only one word long.

[0638] Each token is identified by an address field that stares at bit 7of the first word of the token. The address field is variable in lengthand can potentially extend over multiple words. In a preferredembodiment, the address is no longer than 8 bits long. However, this isnot a limitation on the invention, but on the magnitude of theprocessing steps elected to be accomplished by use of these tokens. Itis to be noted under the extension bit identification label that theextension bit in words 1 and 2 is a 1, signifying that additional wordswill be coming thereafter. The extension bit in word 3 is a zero,therefore indicating the end of that token.

[0639] The token is also capable of variable bit length. For example,there are 9 bits in the token word plus the extension bit for a total of10 bits. In the design of the present invention, output buses are ofvariable width. The output from the Spatial Decoder is 9 bits wide, or10 bits wide when the extension bit is included. In a preferredembodiment, the only token that takes advantage of these extra bits isthe DATA token; all other tokens ignore this extra bit. It should beunderstood that this is not a limitation, but only an implementation.

[0640] Through the use of the DATA token and control tokenconfiguration, it is possible to vary the length of the data beingcarried by these DATA tokens in the sense of the number of bits in oneword. For example, it has been discussed that data bits in Word of aDATA Token can be combined with the data bits in another word of thesame DATA token to form an 11 bit or 10 bit address for use in accessingthe random access memories used throughout this serial decompressionprocessor. This provides an additional degree of variability thatfacilitates a broad range of versatility.

[0641] As previously described, the DATA token carries data from oneprocessing stage to the next. Consequently, the characteristics of thistoken change as it passes through the decoder. For example, at the inputto the Spatial Decoder, DATA Tokens carry bit serial coded video datapacked into 3 bit words. Here, there is no limit to the length of eachtoken. However, to illustrate the versatility of this aspect of theinvention (at the output of the Spatial Decoder circuit), each DATAToken carries exactly 64 words and each word is 9 bits wide. Morespecifically, the standard encoding signal allows for different lengthmessages to encode different intensities and details of pictures. Thefirst picture of a group normally carries the longest number of databits because it needs to provide the most information to the processingunit so that it can start the decompression with as much information aspossible. Words which follow later are typically shorter in lengthbecause they contain the difference signals comparing the first wordwith reference to the second position on the scan information field.

[0642] The words are interspersed with each other, as required by thestandard encoding system, so that variable amounts of data are providedinto the input of the Spatial Decoder. However, after the SpatialDecoder has functioned, the Information is provided at its output at apicture format rate suitable for display on a screen. The output rate interms of time of the spatial decoder may vary in order to interface withvarious display systems throughout the world, such as NTSC, PAL andSECAM. The video formatter converts this variable picture rate to aconstant picture rate suitable for display. However, the picture data isstill carried by DATA tokens consisting of 64 words.

[0643] 11. DRAM Interface

[0644] A single high performance, configurable DRAM interface is used oneach of the 3 decoder chips. In general, the DRAM interface on each chipis substantially the same; however, the interfaces differ from one toanother in how they handle channel priorities. This interface isdesigned to directly drive the external DRAMs used by the SpatialDecoder, the Temporal Decoder and the Video Formatter. Typically, noexternal logic, buffers or components will be required to connect theDRAM interface to the DRAMs in those systems.

[0645] In accordance with the present invention, the interface isconfigurable in two ways:

[0646] 1. The detailed timing of the interface can be configured toaccommodate a variety of different DRAM types.

[0647] 2. The width of the data interface to the DRAM can be configuredto provide a cost/performance trade off for different applications.

[0648] In general, the DRAM interface is a standard-independent blockimplemented on each of the three chips in the system. Again, these arethe Spatial Decoder, Temporal Decoder and video formatter. Referringagain to FIGS. 11, 12 and 13, these figures show block diagrams thatdepict the relationship between the DRAM interface, and the remainingblocks of the Spatial Decoder, Temporal Decoder and video formatter,respectively. On each chip, the DRAM interface connects the chip to anexternal DRAM. External DRAM is used because, at present, it is notpractical to fabricate on chip the relatively large amount of DRAMneeded. Note: each chip has its own external DRAM and its own DRAMinterface.

[0649] Furthermore, while the DRAM interface is compressionstandard-independent, it still must be configured to implement each ofthe multiple standards, H.261, JPEG and MPVr. How the DRAM interface isreconfigured for multi-standard operation will be subsequently furtherdescribed herein.

[0650] Accordingly, to understand the operation of the DRAM interfacerequires an understanding of the relationship between the DRAM interfaceand the address generator, and how the two communicate using the twowire interface.

[0651] In general, as its name implies, the address generator generatesthe addresses the DRAM interface needs in order to address the DRAM(e.g., to read from or to write to a particular address in DRAM). With atwo-wire interface, reading and writing only occurs when the DRAMinterface has both data (from preceding stages in the pipeline), and avalid address (from address generator). The use of a separate addressgenerator simplifies the construction of both the address generator andthe DRAM interface, as discussed further below.

[0652] In the present invention, the DRAM interface can operate from aclock which is asynchronous to both the address generator and to theclocks of the stages through which data is passed. Special techniqueshave been used to handle this asynchronous nature of the operation.

[0653] Data is typically transferred between the DRAM interface and therest of the chip in blocks of 64 bytes (the only exception beingprediction data in the Temporal Decoder) Transfers take place by meansof a device known as a “swing buffer”. This is essentially a pair ofRAMs operated in a double-buffered configuration, with the DRAMinterface filling or emptying one RAM while another part of the chipempties or fills the other RAM. A separate bus which carries an addressfrom an address generator is associated with each swing buffer.

[0654] In the present invention, each of the chips has four swingbuffers, but the function of these swing buffers is different in eachcase. In the spatial decoder, one swing buffer is used to transfer codeddata to the DRAM, another to read coded data from the DRAM, the third totransfer tokenized data to the DRAM and the fourth to read tokenizeddata from the DRAM. In the Temporal Decoder, however, one swing bufferis used to write intra or predicted picture data to the DRAM, the secondto read intra or predicted data from the DRAM and the other two are usedto read forward and backward prediction data. In the video formatter,one swing buffer is used to transfer data to the DRAM and the otherthree are used to read data from the DRAM, one for each of luminance (Y)and the red and blue color difference data (Cr and Cb, respectively).

[0655] The following section describes the operation of a hypotheticalDRAM interface which has one write swing buffer and one read swingbuffer. Essentially, this is the same as the operation of the SpatialDecoder's DRAM interface. The operation is illustrated in FIG. 23.

[0656]FIG. 23 illustrates that the control interfaces between theaddress generator 301, the DRAM interface 302, and the remaining stagesof the chip which pass data are all two wire interfaces. The addressgenerator 301 may either generate addresses as the result of receivingcontrol tokens, or it may merely generate a fixed sequence of addresses(e.g., for the FIFO buffers of the Spatial Decoder). The DRAM interfacetreats the two wire interfaces associated with the address generator 301in a special way. Instead of keeping the accept line high when it isready to receive an address, it waits for the address generator tosupply a valid address, processes that address and then sets the acceptline high for one clock period. Thus, it implements arequest/acknowledge (REQIACK) protocol.

[0657] A unique feature of the DRAM interface 302 is its ability tocommunicate independently with the address generator 301 and with thestages that provide or accept the data. For example, the addressgenerator may generate an address associated with the data in the writeswing buffer (FIG. 24), but no action will be taken until the writeswing buffer signals that there is a block of data ready to be writtento the external DRAM. Similarly, the write swing buffer may contain ablock of data which is ready to be written to the external DRAM, but noaction is taken until an address is supplied on the appropriate bus fromthe address generator 301. Further, once one of the RAMs in the writeswing buffer has been filled with data, the other may be completelyfilled and “swung” to the DRAM interface side before the data input isstalled (the two-wire interface accept signal set low).

[0658] In understanding the operation of the DRAM interface 302 of thepresent invention, it is important to note that in a properly configuredsystem, the DRAM interface will be able to transfer data between theswing buffers and the external DRAM 303 at least as fast as the sum ofall the average data rates between the swing buffers and the rest of thechip.

[0659] Each DRAM interface 302 determines which swing buffer it willservice next. In general, this will either be a “round robin” (i.e., thenext serviced swing buffer is the next available swing buffer which hasleast recently had a turn), or a priority encoder, (i.e., in which someswing buffers have a higher priority than others). In both cases, anadditional request will come from a refresh request generator which hasa higher priority than all the other requests. The refresh request isgenerated from a refresh counter which can be programmed via themicroprocessor interface.

[0660] Referring now to FIG. 24, there is shown a block diagram of awrite swing buffer. The write swing buffer interface includes two blocksof RAM, RAM1 311 and RAM2 312. As discussed further herein, data iswritten into RAM1 311 and RAM2 312 from the previous stage, under thecontrol of the write address 313 and control 314. From RAM1 311 and RAM2312, the data is written into DRAM 515. When writing data into DRAM 315,the DRAM row address is provided by the address generator, and thecolumn address is provided by the write address and control, asdescribed further herein. In operation, valid data is presented at theinput 316 (data in). Typically, the data is received from the previousstage. As each piece of data is accepted by the DRAM interface, it iswritten into RAM1 311 and the write address control increments the RAM1address to allow the next piece of data to be written into RAM1. Datacontinues to be written into RAM1 311 until either there is no moredata, or RAM1 is full. When RAM1 311 is full, the input side gives upcontrol and sends a signal to the read side to indicate that RAM1 is nowready to be read. This signal passes between two asynchronous clockregimes and, therefore, passes through three synchronizing flip flops.

[0661] Provided RAM2 312 is empty, the next item of data to arrive onthe input side is written into RAM2. Otherwise, this occurs when RAM2312 has emptied. When the round robin or priority encoder (depending onwhich is used by the particular chip) indicates that it is now the turnof this swing buffer to be read, the DRAM interface reads the contentsof RAM1 311 and writes them to the external DRAM 315. A signal is thensent back across the asynchronous interface, to indicate that RAM1 311is now ready to be filled again.

[0662] If the DRAM interface empties RAM1 311 and “swings” it before theinput side has filled RAM2 312 , then data can be accepted by the swingbuffer continually. Otherwise, when RAM2 is filled, the Swing bufferwill set its accept single low until RAM1 has been “swung” back for useby the input side.

[0663] The operation of a read swing buffer, in accordance with thepresent invention, is similar, but with the input and output data bussesreversed.

[0664] The DRAM interface of the present invention is designed tomaximize the available memory bandwidth. Each 8×8 block of data isstored in the same DRAM page. In this way, full use can be made of DRAMfast page access modes, where one row address is supplied followed bymany column addresses. In particular, row addresses are supplied by theaddress generator, while column addresses are supplied by the DRAM isinterface, as discussed further below.

[0665] In addition, the facility is provided to allow the data bus tothe external DRAM to be 8, 16 or 32 bits wide. Accordingly, the amountof DRAM used can be matched to the size and bandwidth requirements ofthe particular application.

[0666] In this example (which is exactly how the DRAM interface on theSpatial Decoder works) the address generator provides the DRAM interfacewith block addresses for each of the read and write swing buffers. Thisaddress is used as the row address for the DRAM. The six bits of columnaddress are supplied by the DRAM interface itself, and these bits arealso used as the address for the swing buffer RAM. The data bus to theswing buffers is 32 bits wide. Hence, if the bus width to the externalDRAM is less than 32 bits, two or four external DRAM accesses must bemade before the next word is read from a write swing buffer or the nextword is written to a read swing buffer (read and write refer to thedirection of transfer relative to the external DRAM).

[0667] The situation is lore complex in the case of the Temporal Decoderand the Video Formatter. The Temporal Decoder's addressing is morecomplex because of its predictive aspects as discussed further in thissection. The video formatter's addressing is more complex because ofmultiple video output standard aspects, as discussed further in thesections relating to the video formatter.

[0668] As mentioned previously, the Temporal Decoder has four swingbuffers: two are used to read and write decoded intra and predicted (Iand P) picture data. These operate as described above. The other two areused to receive prediction data. These buffers are more interesting.

[0669] In general, prediction data will be offset from the position ofthe block being processed as specified in the motion vectors in x and y.Thus, the block of data to be retrieved will not generally correspond tothe block boundaries of the data as it was encoded (and written into theDRAM). This is illustrated in FIG. 25, where the shaded area representsthe block that is being formed whereas the dotted outline represents theblock from which it is being predicted. The address generator convertsthe address specified by the motion vectors to a block offset (a wholenumber of blocks), as shown by the big arrow, and a pixel offset, asshown by the little arrow.

[0670] In the address generator, the frame pointer, base block addressand vector offset are added to form the address of the block to beretrieved from the DRAM. If the pixel offset is zero, only one requestis generated. If there is an offset in either the x or y dimension thentwo requests are generated, i.e., the original block address and the oneimmediately below. With an offset in both x and y, four requests aregenerated. For each block which is to be retrieved, the addressgenerator calculates start and stop addresses which is best illustratedby an example.

[0671] Consider a pixel offset of (1,1), as illustrated by the shadedarea in FIG. 26. The address generator makes four requests, labelled Athrough D in the Figure. The problem to be solved is how to provide therequired sequence of row addresses quickly. The solution is to use“start/stop” technology, and this is described below.

[0672] Consider block A in FIG. 26. Reading must start at position (1,1)and end at position (7,7). Assume for the moment that one byte is beingread at a time (i.e., an 8 bit DRAM interface). The x value intheco-ordinate pair forms the three LSBs of the address, the y value thethree MSB. The x and y start values are both 1, providing the address,9. Data is read from this address and the x value is incremented. Theprocess is repeated until the x value reaches its stop value, at whichpoint, the y value is incremented by 1 and the x start value isreloaded, giving an address of 17. As each byte of data is read, the xvalue is again incremented until it reaches its stop value. The processis repeated until both x and y values have reached their stop values.Thus, the address sequence of 9, 10, 11, 12, 13, 14, 15, 17 . . . 23,25, . . . 31, 33 . . . . . , 57, . . . ,63 is generated.

[0673] In a similar manner, the start and stop co-ordinates for block Bare: (1,0) and (7,0), for block C: (0,1) and (0,7), and for block D:(0,0) and (0,0).

[0674] The next issue is where this data should be written. Clearly,looking at block A, the data read from address 9 should be written toaddress 0 in the swing buffer, while the data from address 10 should bewritten to address 1 in the swing buffer, and so on. Similarly, the dataread from address 8 in block B should be written to address 15 in theswing buffer and the data from address 16 should be written to address15 in the swing buffer. This function turns out to have a very simpleimplementation, as outlined below.

[0675] Consider block A. At the start of reading, the swing bufferaddress register is loaded with the inverse of the stop value. The yinverse stop value forms the 3 MSBs and the x inverse stop value formsthe 3 LSB. In this case, while the DRAM interface is reading address 9in the external DRAM, the swing buffer address is zero. The swing bufferaddress register is then incremented as the external DRAM addressregister is incremented, as consistent with proper predictionaddressing.

[0676] The discussion so far has centered on an 8 bit DRAM interface. Inthe case of a 16 or 32 bit interface, a few minor modifications must bemade. First, the pixel offset vector must be “clipped” so that it pointsto a 16 or 32 bit boundary. In the example we have been using, for blockA, the first DRAM read will point to address 0, and data in addresses 0through 3 will be read. Second, the unwanted data must be discarded.This is performed by writing all the data into the swing buffer (whichmust now be physically larger than was necessary in the 8 bit case) andreading with an offset. When performing MPEG half-pel interpolation, 9bytes in x and/or y must be read from the DRAM interface. In this case,the address generator provides the appropriate start and stop addresses.Some additional logic in the DRAM interface is used, but there is nofundamental change in the way the DRAM interface operates.

[0677] The final point to note about the Temporal Decoder DRAM interfaceof the present invention, is that additional information must beprovided to the prediction filters to indicate what processing isrequired on the data. This consists of the following:

[0678] a “last byte” signal indicating the last byte of a transfer (of64,72 or 81 bytes); an H.261 flag;

[0679] a bidirectional prediction flag;

[0680] two bits to indicate the block's dimensions (8 or 9 bytes in xand y); and

[0681] a two bit number to indicate the order of the blocks.

[0682] The last byte flag can be generated as the data is read out ofthe swing buffer. The other signals are derived from the addressgenerator and are piped through the DRAM interface so that they areassociated with the correct block of data as it is read out of the swingbuffer by the prediction filter block.

[0683] In the Video Formatter, data is written into the external DRAM inblocks, but is read out in raster order. Writing is exactly the same asalready described for the Spatial Decoder, but reading is a little morecomplex.

[0684] The data in the Video Formatter, external DRAM is organized sothat at least 8 blocks of data fit into a single page. These 8 blocksare 8 consecutive horizontal blocks. When rasterizing, 8 bytes need tobe read out of each of a consecutive blocks and written into the swingbuffer (i.e., the same row in each of the 8 blocks).

[0685] Considering the top row (and assuming a byte-wide interface), thex address (the three LSBS) is set to zero, as is the y address (3 MSBS).The x address is then incremented as each of the first 8 bytes are readout. At this point, the top part of the address (bit 6 and above−LSB=bit0) is incremented and the x address (3 LSBS) is reset to zero. Thisprocess is repeated until 64 bytes have been read. With a 16 or 32 bitwide interface to the external DRAM the x address is merely incrementedby two or four, respectively, instead of by one.

[0686] In the present invention, the address generator can signal to theDRAM interface that less than 64 bytes should be read (this may berequired at the beginning or end of a raster line), although a multipleof 8 bytes is always read. This is achieved by using start and stopvalues. The start value is used for the top part of the address (bit 5and above), and the stop value is compared with the start value togenerate the signal which indicates when reading should stop.

[0687] The DRAM interface timing block in the present invention usestiming chains to place the edges of the DRAM signals to a precision of aquarter of the system clock period. Two quadrature clocks from the phaselocked loop are used. These are combined to form a notional 2x clock.Any one chain is then made from two shift registers in parallel, onopposite phases of the 2x clock.

[0688] First of all, there is one chain for the page start cycle andanother for the read/write/refresh cycles. The length of each cycle isprogrammable via the microprocessor interface, after which the pagestart chain has a fixed length, and the cycle chain's length changes asappropriate during a page start.

[0689] On reset, the chains are cleared and a pulse is created. Thepulse travels along the chains and is directed by the state informationfrom the DRAM interface. The pulse generates the DRAM interface clock.Each DRAM interface clock period corresponds to one cycle of the DRAM,consequently, as the DRAM cycles have different lengths, the DRAMinterface clock is not at a constant rate.

[0690] Moreover, additional timing chains combine the pulse from theabove chains with the information from the DRAM interface to generatethe output strobes and enables such as notcas, notras, notwe, notbe.

[0691] 12. Prediction Filters

[0692] Referring again to FIGS. 12, 17, 18, and more particularly toFIG. 12, there is shown a block diagram of the Temporal Decoder. Thisincludes the prediction filter. The relationship between the predictionfilter and the rest of the elements of the temporal decoder is shown ingreater detail in FIG. 17. The essence of the structure of theprediction filter is shown in FIGS. 18 and 28. A detailed description ofthe operation of the prediction filter can be found in the section,“More Detailed Description of the Invention.”

[0693] In general, the prediction filter in accordance with the presentinvention, is used in the MPEG and H.261 modes, but not in the JPEGmode. Recall that in the JPEG mode, the Temporal Decoder just passes thedata through to the Video Formatter, without performing any substantivedecoding beyond that accomplished by the Spatial Decoder. Referringagain to FIG. 18, in the MPEG mode the forward and backward predictionfilters are identical and they filter the respective MPEG forward andbackward prediction blocks. In the H.261 mode, however, only the forwardprediction filter is used, since H.261 does not use backward prediction.

[0694] Each of the two prediction filters of the present invention issubstantially the same. Referring again to FIGS. 18 and 28 and moreparticularly to FIG. 28, there is shown a block diagram of the structureof a prediction filter. Each prediction filter consists of four stagesin series. Data enters the format stage 331 and is placed in a formatthat can be readily filtered. In the next stage 332 an I-D prediction isperformed on the X-coordinate. After the necessary transposition isperformed by a dimension buffer stage 333, an I-D prediction isperformed on the Y-coordinate in stage 334. How the stage perform thefiltering is further described in greater detail subsequently. Whichfiltering operations are required, are defined by the compressionstandard. In the case of H.261, the actual filtering performed issimilar to that of a low pass filter.

[0695] Referring again to FIG. 17, multi-standard operation requiresthat the prediction filters be reconfigurable to perform either MPEG orH.261 filtering, or to perform no filtering at all in JPEG mode. As withmany other reconfigurable aspects of the three chip system, theprediction filter is reconfigured by means of tokens. Tokens are alsoused to inform the address generator of the particular mode ofoperation. In this way, the address generator can supply the predictionfilter with the addresses of the needed data, which varies significantlybetween MPEG and JPEG.

[0696] 13. Accessing Registers

[0697] Most registers in the microprocessor interface (MPI) can only bemodified if the stage with which they are associated is stopped.Accordingly, groups of registers will typically be associated with anaccess register. The value zero in an access register indicates that thegroup of registers associated with that particular access registershould not be modified. Writing 1 to an access register requests that astage be stopped. The stage may not stop immediately, however, so thestages access register will hold the value, zero, until it is stopped.

[0698] Any user software associated with the MPI and used to performfunctions by way of the MPI should wait “after writing a 1 to a requestaccess register” until 1 is read from the access register. If a userwrites a value to a configuration register while its access register isset to zero, the results are undefined.

[0699] 14. Micro-processor Interface

[0700] A standard byte wide micro-processor interface (MPI) is used onall circuits with in the Spatial Decoder and Temporal Decoder. The MPIoperates asynchronously with various Spatial and Temporal Decoderclocks. Referring to Table A.6.1 of the subsequent further detaileddescription, there is shown the various MPI signals that are used onthis interface. The character of the signal is shown on the input/outputcolumn, the signal name is shown on the signal name column and adescription of the function of the signal is shown in the descriptioncolumn. The MPI electrical specification are shown with reference toTable A.6.2. All the specifications are classified according to type andthere types are shown in the column entitled symbol. The description ofwhat these symbols represent is shown in the parameter column. Theactual specifications are shown in the respective columns min, max andunits.

[0701] The DC operating conditions can be seen with reference to TableA.6.3. Here the column headings are the same as with reference to TableA.6.2. The DC electrical characteristics are shown with reference toTable A.6.4 and carry the same column headings as depicted in TablesA.6.2 and A.6.3.

[0702] 15. XPI Read Timing

[0703] The AC characteristics of the MPI read timing diagrams are shownwith reference to FIG. 54. Each line of the Figure is labelled with acorresponding signal name and the timing is given in nano-seconds. Thefull microprocessor interface read timing characteristics are shown withreference to Table A.6.5. The column entitled Number is used to indicatethe signal corresponding to the name of that signal as set forth in thecharacteristic column. The columns identified by MIN and MAX provide theminimum length of time that the signal is present the maximum amount oftime that this signal is available. The Units column gives the units ofmeasurement used to describe the signals.

[0704] 16. MPI Write Timing

[0705] The general description of the MPI write timing diagrams areshown with reference to FIG. 54. This Figure shows each individualsignal name as associated with the MPI write timing. The name, thecharacteristic of the signal, and other various physical characteristicsare shown with reference to Table 6.6.

[0706] 17. Keyhole Address Locations

[0707] In the present invention, certain less frequently accessed memorymap locations have been placed behind keyhole registers. A keyholeregister has two registers associated with it. The first register is akeyhole address register and the second register is a keyhole dataregister. The keyhole address specifies a location within a extendedaddress space. A read or a write operation to a keyhole data registeraccesses the locations specified by the keyhole address register. Afteraccessing a keyhole data register, the associated keyhole addressregister increments. Random access within the extended address space isonly possible by writing in a new value to the keyhole address registerfor each access. A circuit within the present invention may have morethan one keyhole memory maps. Nonetheless, there is no interactionbetween the different keyholes.

[0708] 18. Picture-end

[0709] Referring again to FIG. 11, there is shown a general blockdiagram of the Spatial Decoder used in the present invention. It isthrough the use of this block diagram that the function of PICTURE ENDwill be described. The PICTURE_END function has the multi-standardadvantage of being able to handle H.261 encoded picture information,MPEG and JPEG signals.

[0710] As previously described, the system of FIG. 11 is interconnectedby the two wire interface previously described. Each of the functionalblocks is arranged to operate according to the state machineconfiguration shown with reference to FIG. 10.

[0711] In general, the PICTURE_END function in accordance with theinvention begins at the Start Code Detector which generates aPICTURE_END control token. The PICTURE_END control token is passedunaltered through the start-up control circuit to the DRAM interface.Here it is used to flush out the write swing buffers in the DRAMinterface. Recall, that the contents of a swing buffer are only writtento RAM when the buffer is full. However, a picture may end at a pointwhere the buffer is not full, therefore, causing the picture data tobecome stuck. The PICTURE_END token forces the data out of the swingbuffer.

[0712] Since the present invention is a multi-standard machine, themachine operates differently for each compression standard. Moreparticularly, the machine is fully described as operating pursuant tomachine-dependent action cycles. For each compression standard, acertain number of the total available action cycles can be selected by acombination of control tokens and/or output signals from the MPU or theycan be selected by the design of the control tokens themselves. In thisregard, the present invention is organized so as to delay theinformation from going into subsequent blocks until all of theinformation has been collected in an upstream block. The system waitsuntil the data has been prepared for passing to the next stage. In thisway, the PICTURE END signal is applied to the coded data buffer, and thecontrol portion of the PICTURE_END signal causes the contents of thedata buffers to be read and applied to the Huffman decoder and videodemultiplexor circuit.

[0713] Another advantage of the PICTURE_END control token is toidentify, for the use by the Huffman decoder demultiplexor, the end ofpicture even though it has not had the typically expected full rangeand/or number of signals applied to the Huffman decoder and videodemultiplexor circuit. In this situation, the information held in thecoded data buffer is applied to the Huffman decoder and videodemultiplexor as a total picture. In this way, the state machine of theHuffman decoder and video demultiplexor can still handle the dataaccording to system design.

[0714] Another advantage of the PICTURE_END control token is its abilityto completely empty the coded data buffer so that no stray informationwill inadvertently remain in the off chip DRAM or in the swing buffers.

[0715] Yet another advantage of the PICTURE_END function is its use inerror recovery. For example, assume the amount of data being held in thecoded data buffer is less than is typically used for describing thespatial information with reference to a single picture. Accordingly, thelast picture will be held in the data buffer until a full swing buffer,but, by definition, the buffer will never fill. At some point, themachine will determine that an error condition exits. Hence, to theextent that a PICTURE_END token is decoded and forces the data in thecoded data buffers to be applied to the Huffman decoder and videodemultiplexor, the final picture can be decoded and the informationemptied from the buffers. Consequently, the machine will not go intoerror recovery mode and will successfully continue to process the codeddata.

[0716] A still further advantage of the use of a PICTURE_END token isthat the serial pipeline processor will continue the processing ofuninterrupted data. Through the use of a PICTURE_END token, the serialpipeline processor is configured to handle less than the expected amountof data and, therefore, continues processing. Typically, a prior artmachine would stop itself because of an error condition. As previouslydescribed, the coded data buffer counts macroblocks as they come intoits storage area. In addition, the Huffman Decoder and VideoDemultiplexor generally know the amount of information expected fordecoding each picture, i.e., the state machine portion of the Huffmandecode and Video Demultiplexor know the number of blocks that it willprocess during each picture recovery cycle. When the correct number ofblocks do not arrive from the coded data buffer, typically an errorrecovery routine would result. However, with the PICTURE_END controltoken having reconfigured the Huffman Decoder and Video Demultiplexor,it can continue to function because the reconfiguration tells theHuffman Decoder and Video Demultiplexor that it is, indeed, handling theproper amount of information.

[0717] Referring again to FIG. 10, the Token Decoder portion of theBuffer Manager detects the PICTURE_END control token generated by theStart Code Detector. Under normal operations, the buffer registers fillup and are emptied, as previously described with reference to the normaloperation of the swing buffers. Again, a swing buffer which is partiallyfull of data will not empty until it is totally filled and/or it knowsthat it is time to empty. The PICTURE_END control token is decoded inthe Token Decoder portion of the Buffer Manager, and it forces thepartially full swing buffer to empty itself into the coded data buffer.This is ultimately passed to the Huffman Decoder and Video Demultiplexoreither directly or through the DRAM interface.

[0718] 19. Flushing Operation

[0719] Another advantage of the PICTURE_END control token is itsfunction in connection with a FLUSH token. The FLUSH token is notassociated with either controlling the reconfiguration of the statemachine or in providing data for the system. Rather, it completes priorpartial signals for handling by the machine-dependent state machines.Each of the state machines recognizes a FLUSH control token asinformation not to be processed. Accordingly, the FLUSH token is used tofill up all of the remaining empty parts of the coded data buffers andto allow a full set of information to be sent to the Huffman Decoder andVideo Demultiplexor. In this way, the FLUSH token is like padding forbuffers.

[0720] The Token Decoder in the Huffman circuit recognizes the FLUSHtoken and ignores the pseudo data that the FLUSH token has forced intoit. The Huffman Decoder then operates only on the data contents of thelast picture buffer as it existed prior to the arrival of thePICTURE_END token and FLUSH token. A further advantage of the use of thePICTURE END token alone or in combination with a FLUSH token is thereconfiguration and/or reorganization of the Huffman Decoder circuit.With the arrival of the PICTURE_END token, the Huffman Decoder circuitknows that it will have less information than normally expected todecode the last picture. The Huffman decode circuit finishes processingthe information contained in the last picture, and outputs thisinformation through the DRAM interface into the Inverse Modeller. Uponthe identification of the last picture, the Huffman Decoder goes intoits cleanup mode and readjusts for the arrival of the next pictureinformation.

[0721] 24. Flush Function

[0722] The FLUSH token, in accordance with the present invention, isused to pass through the entire pipeline processor and to ensure thatthe buffers are emptied and that other circuits are reconfigured toawait the arrival of new data. More specifically, the present inventioncomprises a combination of a PICTURE_END token, a padding word and aFLUSH token indicating to the serial pipeline processor that the pictureprocessing for the current picture form is completed. Thereafter, thevarious state machines need reconfiguring to await the arrival of newdata for new handling. Note also that the FLUSH Token acts as a specialreset for the system. The FLUSH token resets each stage as it passesthrough, but allows subsequent stages to continue processing. Thisprevents a loss of data. In other words, the FLUSH token is a variablereset, as opposed to, an absolute reset.

[0723] 21. Stop-after Picture

[0724] The STOP_AFTER_PICTURE function is employed to shut down theprocessing of the serial pipeline decompressing circuit at a logicalpoint in its operation. At this point, a PICTURE_END token is generatedindicating that data is finished coming in from the data input line, andthe padding operation has been completed. The padding function fillspartially empty DATA tokens. A FLUSH token is then generated whichpasses through the serial pipeline system and pushes all the informationout of the registers and forces the registers back into their neutralstand-by condition. The STOP_AFTER_PICTURE event is then generated andno more input is accepted until either the user or the system clearsthis state. In other words, while a PICTURE_END token signals the end ofa picture, the STOP_AFTER_PICTURE operation signals the end of allcurrent processing.

[0725] 22. Multi-standard—Search Mode

[0726] Another feature of the present invention is the use of aSEARCH_MODE control token which is used to reconfigure the input to theserial pipeline processor to look at the incoming bit stream. When thesearch mode is set, the Start Code Detector searches only for a specificstart code or marker used in any one of the compression standards. Itwill be appreciated, however, that, other images from other databitstreams can be used for this purpose. Accordingly, these images canbe used throughout this present invention to change it to anotherembodiment which is capable of using the combination of control tokens,and DATA tokens along with the reconfiguration circuits, to providesimilar processing.

[0727] The use of search mode in the present invention is convenient inmany situations including 1) if a break in the data bit stream occurs;2) when the user breaks the data bit stream by purposely changingchannels, e.g., data arriving, by a cable carrying compressed digitalvideo; or 3) by user activation of fast forward or reverse from acontrollable data source such as an optical disc or video disc. Ingeneral, a search mode is convenient when the user interrupts the normalprocessing of the serial pipeline at a point where the machine does notexpect such an interruption.

[0728] When any of the search modes are set, the Start Code Detectorlooks for incoming start images which are suitable for creating themachine independent tokens. All data coming into the Start Code Detectorprior to the identification of standard-dependent start images isdiscarded as meaningless and the machine stands in an idling conditionas it waits this information.

[0729] The Start Code Detector can assume any one of a number ofconfigurations. For example, one of these configurations allows a searchfor a group of pictures or higher start codes. This pattern causes theStart Code Detector to discard all its input and look for thegroup_start standard image. When such an image is identified, the StartCode Detector generates a GROUP_START token and the search mode is resetautomatically.

[0730] It is important to note that a single circuit, the HuffmanDecoder and Video Demultiplex circuit, is operating with a combinationof input signals including the standard-independent set-up signals, aswell as, the CODING_STANDARD signals. The CODING_STANDARD signals areconveying information directly from the incoming bit stream as requiredby the Huffman Decoder and Video Demultiplex circuit. Nevertheless,while the functioning of the Huffman Decoder and Video Demultiplexcircuit is under the operation of the standard independent sequence ofsignals.

[0731] This mode of operation has been selected because it is the mostefficient and could have been designed wherein special control tokensare employed for conveying the standard-dependent input to the HuffmanDecoder and Video Demultiplexer instead of conveying the actual signalsthemselves.

[0732] 23. Inverse Modeller

[0733] Inverse modeling is a feature of all three standards, and is thesame for all three standards. In general, DATA tokens in the tokenbuffer contain information about the values of the quantizedcoefficients, and about the number of zeros between the coefficientsthat are represented (a form of run length coding). The Inverse Modellerof the present invention has been adapted for use with tokens and simplyexpands the information about runs of zeros so that each DATA Tokencontains-the requisite 64 values. Thereafter, the values in the DATATokens are quantized coefficients which can be used by the InverseQuantizer.

[0734] 24. Inverse Quantizer

[0735] The Inverse Quantizer of the present invention is a requiredelement in the decoding sequence, but has been implemented in such awayto allow the entire IC set to handle multi-standard data. In addition,the Inverse Quantizer has been adapted for use with tokens. The InverseQuantizer lies between the Inverse modeller and inverse DCT (IDCT).

[0736] For example, in the present invention, an adder in the InverseQuantizer is used to add a constant to the pel decode number before thedata moves on to the IDCT.

[0737] The IDCT uses the pel decode number, which will vary according toeach standard used to encode the information. In order for theinformation to be properly decoded, a value of 1024 is added to thedecode number by the Inverse Quantizer before the data continues on tothe IDCT.

[0738] Using adders, already present in the Inverse Quantizer, tostandardize the data prior to it reaching the IDCT, eliminates the needfor additional circuitry or software in the IC, for handling datacompressed by the various standards. Other operations allowing formulti-standard operation are performed during a “post quantizationfunction” and are discussed below.

[0739] The control tokens accompanying the data are decoded and thevarious standardization routines that need to be performed by theInverse Quantizer are identified in detail below. These “postquantization” functions are all implemented to avoid duplicate circuitryand to allow the IC to handle multi-standard encoded data.

[0740] 25. Huffman Decoder and Parser

[0741] Referring again to FIGS. 11 and 27, the Spatial Decoder includesa Huffman Decoder for decoding the data that the various compressionstandards have Huffman-encoded. While each of the standards, JPEG, MPEGand H.261, require certain data to be Huffman encoded, the Huffmandecoding required by each standard differs in some significant ways. Inthe Spatial Decoder of the present invention, rather than design andfabricate three separate Huffman decoders, one for each standard, thepresent invention saves valuable die space by identifying common aspectsof each Huffman Decoder, and fabricating these common aspects only once.Moreover, a clever multi-part algorithm is used that makes common moreaspects of each Huffman Decoder common to the other standards as wellthan would otherwise be the case.

[0742] In brief, the Huffman Decoder 321 works in conjunction with theother units shown in FIG. 27. These other units are the Parser StateMachine 322, the inshifter 323, the Index to Data unit 324, the ALU 325,and the Token Formatter 326. As described previously, connection betweenthese blocks is governed by a two wire interface. A more detaileddescription of how these units function is subsequently described hereinin greater detail, the focus here is on particular aspects of theHuffman Decoder, in accordance with the present invention, that supportmulti-standard operation.

[0743] The Parser State Machine of the present invention, is aprogrammable state machine that acts to coordinate the operation of theother blocks of the Video Parser. In response to data, the Parser StateMachine controls the other system blocks by generating a control wordwhich is passed to the other blocks, side by side with the data, uponwhich this control word acts. Passing the control word alongside theassociated data is not only useful, it is essential, since these blocksare connected via a two-wire interface. In this way, both data andcontrol arrive at the same time. The passing of the control word isindicated in FIG. 27 by a control line 327 that runs beneath the dataline 328 that connects the blocks. Among other things, this code wordidentifies the particular standard that is being decoded.

[0744] The Huffman decoder 321 also performs certain control functions.In particular, the Huffman Decoder 321 contains a state machine that cancontrol certain functions of the Index to Data 324 and ALU 325. Controlof these units by the Huffman Decoder is necessary for proper decodingof block-level information. Having the Parser State Machine 322 makethese decisions would take too much time.

[0745] An important aspect of the Huffman Decoder of the presentinvention, is the ability to invert the coded data bits as they are readinto the Huffman Decoder. This is needed to decode H.261 style Huffmancodes, since the particular type of Huffman code used by H.261 (andsubstantially by MPEG) has the opposite polarity then the codes used byJPEG. The use of an inverter, thereby, allows substantially the sametable to be used by the Huffman Decoder for all three standards. Otheraspects of how the Huffman Decoder implements all three standards arediscussed in further detail in the “More Detailed Description of theInvention” section.

[0746] The Index to Data unit 324 performs the second part of themulti-part algorithm. This unit contains a look up table that providesthe actual Huffman decoded data. Entries in the table are organizedbased on the index numbers generated by the Huffman Decoder.

[0747] The ALU 325 implements the remaining parts of the multi-partalgorithm. In particular, the ALU handles sign-extension. The ALU alsoincludes a register file which holds vector predictions and DCpredictions, the use of which is described in the sections related toprediction filters. The ALU, further, includes counters that countthrough the structure of the picture being decoded by the SpatialDecoder. In particular, the dimensions of the picture are programmedinto registers associated with the counters, which facilitates detectionof “start of picture,” and start of macroblock codes.

[0748] In accordance with the present invention, the Token Formatter 326(TF) assembles decoded data into DATA tokens that are then passed ontothe remaining stages or blocks in the Spatial Decoder.

[0749] In the present invention, the in shifter 323 receives data from aFIFO that buffers the data passing through the Start Code Detector. Thedata received by the inshifter is generally of two types: DATA tokens,and start codes which the Start Code Detector has replaced with theirrespective tokens, as discussed further in the token section. Note thatmost of the data will be DATA tokens that require decoding.

[0750] The ln shifter 323 serially passes data to the Huffman Decoder321. On the other hand, it passes control tokens in parallel. In theHuffman decoder, the Huffman encoded data is decoded in accordance withthe first part of the multi-part algorithm. In particular, theparticular Huffman code is identified, and then replaced with an indexnumber.

[0751] The Huffman Decoder 321 also identifies certain data thatrequires special handling by the other blocks shown in FIG. 27. Thisdata includes end of block and escape. In the present invention, time issaved by detecting these in the Huffman Decoder 321, rather than in theIndex to Data unit 324.

[0752] This index number is then passed to the Index to Data unit 324.In essence, the Index to Data unit is a look-up table. In accordancewith one aspect of the algorithm, the look-up table is little more thanthe Huffman code table specified by JPEG. Generally, it is in thecondensed data format that JPEG specifies for transferring an alternateJPEG table.

[0753] From the Index to Data unit 324, the decoded index number orother data is passed, together with the accompanying control word, tothe ALU 325, which performs the operations previously described.

[0754] From the-ALU 325, the data and control word is passed to theToken Formatter 326 (TF). In the Token Formatter, the data is combinedas needed with the control word to form tokens. The tokens are thenconveyed to the next stages of the Spatial Decoder. Note that at thispoint, there are as many tokens as will be used by the system.

[0755] 26. Inverse Discrete Cosine Transform

[0756] The Inverse Discrete Cosine Transform (IDCT), in accordance withthe present invention, decompresses data related to the frequency of theDC component of the picture. When a particular picture is beingcompressed, the frequency of the light in the picture is quantized,reducing the overall amount of information needed to be stored. The IDCTtakes this quantized data and decompresses it back into frequencyinformation.

[0757] The IDCT operates on a portion of the picture which is 8×8 pixelsin size. The math which performed on this data is largely governed bythe particular standard used to encode the data. However, in the presentinvention, significant use is made of common mathematical functionsbetween the standards to avoid unnecessary duplication of circuitry.

[0758] Using a particular scaling order, the symmetry between the upperand lower portions of the algorithms is increased, thus commonmathematical functions can be reused which eliminates the need foradditional circuitry.

[0759] The IDCT responds to a number of multi-standard tokens. The firstportion of the IDCT checks the entering data to ensure that the DATAtokens are of the correct size for processing. In fact, the token streamcan be corrected in some situations if the error is-not too large.

[0760] 27. Buffer Manager

[0761] The Buffer Manager of the present invention, receives incomingvideo information and supplies the address generators with informationon the timing of the datas arrival, display and frame rate. Multiplebuffers are used to allow changes in both the presentation and displayrates. Presentation and display rates will typically vary in accordancewith the data that was encoded and the monitor on which the informationis being displayed. Data arrival rates will generally vary according toerrors in encoding, decoding or the source material used to create thedata. When information arrives at the Buffer Manager, it isdecompressed. However, the data is in an order that is useful for thedecompression circuits, but not for the particular display unit beingused. When a block of data enters the Buffer Manager, the Buffer Managersupplies information to the address generator so that the block of datacan be placed in the order that the display device can use. In doingthis, the Buffer Manager takes into account the frame rate conversionnecessary to adjust the incoming data blocks so they are presentable onthe particular display device being used.

[0762] In the present invention, the Buffer Mnager primarily suppliesinformation to the address generators. Nevertheless, it is also requiredto interface with other elements of the system. For example, there is aninterface with an input FIFO which transfers tokens to the BufferManager which, in turn, passes these tokens on to the write addressgenerators.

[0763] The Buffer Manager also interfaces with the display addressgenerators, receiving information on whether the display device is readyto display new data. The Buffer Manager also confirms that the displayaddress generators have cleared information from a buffer for display.

[0764] The Buffer Manager of the present invention keeps track ofwhether a particular buffer is empty, full, ready for use or in use. Italso keeps track of the presentation number associated with theparticular data in each buffer. In this way, the Buffer Managerdetermines the states of the buffers, in part, by making only one bufferat a time ready for display. Once a buffer is displayed, the buffer isin a “vacant” state. When the Buffer Manager receives a PICTURE_START,FLUSH, valid or access token, it determines the status of each bufferand its readiness to accept new data. For example, the PICTURE_STARTtoken causes the Buffer Manager to cycle through each buffer to find onewhich is capable of accepting the new data.

[0765] The Buffer Manager can also be configured to handle themulti-standard requirements dictated by the tokens it receives. Forexample, in the H.261 standard, data maybe skipped during display. Ifsuch a token arrives at the Buffer Manager, the data to be skipped willbe flushed from the buffer in which it is stored.

[0766] Thus, by managing the buffers, data can be effectively displayedaccording to the compression standard used to encode the data, the rateat which the data is decoded and the particular type of display devicebeing used.

[0767] The foregoing description is believed to adequately describe theoverall concepts, system implementation and operation of the variousaspects of the invention in sufficient detail to enable one of ordinaryskill in the art to make and practice the invention with all of itsattendant features, objects and advantages. However, in order tofacilitate a further, more detailed in depth understanding of theinvention, and additional details in connection with even more specific,commercial implementation of various embodiments of the invention, thefollowing further description and explanation is preferred.

[0768] This is a more detailed description for a multi-standard videodecoder chip-set. It is divided into three main sections: A, B and C.

[0769] Again, for purposes of organization, clarity and convenience ofexplanation, this additional disclosure is set forth in the followingsections.

[0770] Description of features common to chips in the chip-set:

[0771] Tokens

[0772] Two wire interfaces

[0773] DRAM interface

[0774] Microprocessor interface

[0775] Clocks

[0776] Description of the Spatial Decoder chip

[0777] Description of the Temporal Decoder chip

[0778] Section A.1

[0779] The first description section covers the majority of theelectrical design issues associated with using the chip-set.

[0780] A.1.1 Typographic conventions

[0781] A small set of typographic conventions is used to emphasize someclasses of information:

[0782] NAMES_OF_TOKENS

[0783] wire_name active high signal

[0784] wire_name active low signal

[0785] register_name

[0786] Section A.2 Video Decoder Family

[0787] 30 MHz operation

[0788] Decodes MPEG, JPEG & H.261

[0789] Coded data rates to 25 Mb/s

[0790] Video data rates to 21 MB/s

[0791] MPEG resolutions up to 704×480, 30 Hz, 4:2:0

[0792] Flexible chroma sampling formats

[0793] Full JPEG baseline decoding

[0794] Glue-less page mode DRAM interface

[0795] 208 pin PQFP package

[0796] Independent coded data and decoder clocks

[0797] Re-orders MPEG picture sequence

[0798] The Video decoder family provides a low chip count solution forimplementing high resolution digital video decoders. The chip-set iscurrently configurable to support three different video and picturecoding systems: JPEG, MPEG and H.261.

[0799] Full JPEG baseline picture decoding is supported. 720×480, 30 Hz,4:2:2 JPEG encoded video can be decoded in real-time.

[0800] CIF (Common Interchange Format) and QCIF H.261 video can bedecoded. Full feature MPEG video with formats up to 740×480, 30 Hz,4:2:0 can be decoded.

[0801] Note: The above values are merely illustrative, by way of exampleand not necessarily by way of limitation, of one embodiment of thepresent invention. Accordingly, it will be appreciated that other valuesand/or ranges may be used.

[0802] A.2.1 System Configurations

[0803] A.2.1.1 Output Formatting

[0804] In each of the examples given below, some form of outputformatter will be required to take the data presented at the output ofthe Spatial Decoder or Temporal Decoder and re-format it for a computeror display system. The details of this formatting will vary betweenapplications. In a simple case, all that is required is an addressgenerator to take the block formatted data output by the decoder chipand write it into memory in a raster order.

[0805] The Image Formatter is a single chip VLSI device providing a widerange of output formatting functions.

[0806] A.2.1.2 JPEG Still Picture Decoding

[0807] A single Spatial Decoder, with no-off-chip DRAM, can rapidlydecode baseline JPEG images. The Spatial Decoder will support allfeatures of baseline JPEG. However, the image size that can be decodedmay be limited by the size of the output buffer provided by the user.The characteristics of the output formatter may limit the chromasampling formats and color spaces that can be supported.

[0808] A.2.1.3 JPEG Video Decoding

[0809] Adding off-chip DRAMs to the Spatial Decoder allows it to decodeJPEG encoded video pictures in real-time. The size and speed of therequired buffers will depend on the video and coded data rates. TheTemporal Decoder is not required to decode JPEG encoded video. However,if a Temporal Decoder is present in a multi-standard decoder chip-set,it will merely pass the data through the Temporal Decoder withoutalteration or modification when the system is configured for JPEGoperation.

[0810] A.2.1.4 H.261 Decoding

[0811] The Spatial Decoder and the Temporal Decoder are both required toimplement an H.261 video decoder. The DRAM interfaces on both devicesare configurable to allow the quantity of DRAM required for properoperation to be reduced when working with small picture formats and atlow coded data rates. Typically, a single 4 Mb (e.g. 512k×8) DRAM willbe required by each of the Spatial Decoder and the Temporal Decoder.

[0812] A.2.1.5 MPEG Decoding

[0813] The configuration required for MPEG operation is the same as forH.261. However, as will be appreciated by one of ordinary skill in theart, larger DRAM buffers may be required to support the larger pictureformats possible with MPEG.

[0814] Section A.3 Tokens

[0815] A.3.1 Token Format

[0816] In accordance with the present invention, tokens provide anextensible format for communicating information through the decoderchip-set. While in the present invention, each word of a Token is aminimum of 8 bits wide, one of ordinary skill in the art will appreciatethat tokens can be of any width. Furthermore, a single Token can bespread over one or more words; this is accomplished using an extensionbit in each word. The formats for the tokens are summarized in TableA.3.1.

[0817] The extension bit indicates whether a Token continues intoanother word. It is set to 1 in all words of a Token except the lastone. If the first word of a Token has an extension bit of 0, thisindicates that the Token is only one word long.

[0818] Each Token is identified by an Address Field that starts in bit 7of the first word of the Token. The Address Field is of variable lengthand can potentially extend over multiple words (in the current chips noaddress is more than 8 bits long, however, one of ordinary skill in theart will again appreciate that addresses can be of any length).

[0819] Some interfaces transfer more than 8 bits of data. For example,the output of the Spatial Decoder is 9 bits wide (10 bits including theextension bit). The only Token that takes advantage of these extra bitsis the DATA Token. The DATA Token can have as many bits as are necessaryfor carrying out processing at a particular place in the system. Allother Tokens ignore the extra bits.

[0820] A.3.2 ” The DATA Token

[0821] The DATA Token carries data from one processing stage to thenext. Consequently, the characteristics of this Token change as itpasses through the decoder. Furthermore, the meaning of the data carriedby the DATA Token varies depending on where the DATA Token is within thesystem, i.e., the data is position dependent. In this regard, the datamay be either frequency domain or Pel domain data depending on where theDATA Token is within the Spatial Decoder. For example, at the input ofthe Spatial Decoder, DATA Tokens carry bit serial coded video datapacked into 8 bit words. At this point, there is no limit to the lengthof each Token. In contrast, however, at the output of the SpatialDecoder each DATA Token carries exactly 64 words and each word is 9 bitswide.

[0822] A.3.3 Using Token Formatted Data

[0823] In some applications, it may be necessary for the circuitry thatconnect directly to the input or output of the Decoder or chip set. Inmost cases it will be sufficient to collect DATA Tokens and to detect afew Tokens that provide synchronization information (such as PICTURESTART). In this regard, see subsequent sections A.16, ” Connecting tothe output of Spatial Decoder”, and A.19, ” Connecting to the output ofthe Temporal Decoder”.

[0824] As discussed above, it is sufficient to observe activity on theextension bit to identify when each new Token starts. Again, theextension bit signals the last word of the current token. In addition,the Address field can be tested to identify the Token. Unwanted orunrecognized Tokens can be consumed (and discarded) without knowledge oftheir content. However, a recognized token causes an appropriate actionto occur.

[0825] Furthermore, the data input to the Spatial Decoder can either besupplied as bytes of coded data, or in DATA Tokens (see Section A.10, ”Coded data input”). Supplying Tokens via the coded data port or via themicroprocessor interface allows many of the features of the decoder chipset to be configured from the data stream. This provides an alternativeto doing the configuration via the micro processor interface. TABLEA.3.1 Summary of Tokens 7 6 5 4 3 2 1 0 Token Name Reference 0 0 1QUANT_SCALE 0 1 0 PREDICTION_MODE 0 1 1 (reserved) 1 0 0 MVD_FORWARDS 10 1 MVD_BACKWARDS 0 0 0 0 1 QUANT_TABLE 0 0 0 0 0 1 DATA 1 1 0 0 0 0COMPONENT_NAME 1 1 0 0 0 1 DEFINE_SAMPLING 1 1 0 0 1 0 JPEG_TABLE_SELECT1 1 0 0 1 1 MPEG_TABLE_SELECT 1 1 0 1 0 0 TEMPORAL_REFERENCE 1 1 0 1 0 1MPEG_DCH_TABLE 1 1 0 1 1 0 (reserved) 1 1 0 1 1 1 (reserved) 1 1 1 0 0 00 (reserved) SAVE_STATE 1 1 1 0 0 0 1 (reserved) RESTORE_STATE 1 1 1 0 01 0 TIME_CODE 1 1 1 0 0 1 1 (reserved) 0 0 0 0 0 0 0 0 NULL 0 0 0 0 0 00 1 (reserved) 0 0 0 0 0 0 1 0 (reserved) 0 0 0 0 0 0 1 1 (reserved) 0 00 1 0 0 0 0 SEQUENCE_START 0 0 0 1 0 0 0 1 GROUP_START 0 0 0 1 0 0 1 0PICTURE_START 0 0 0 1 0 0 1 1 SLICE_START 0 0 0 1 0 1 0 0 SEQUENCE_END 00 0 1 0 1 0 1 CODING_STANDARD 0 0 0 1 0 1 1 0 PICTURE_END 0 0 0 1 0 1 11 FLUSH 0 0 0 1 1 0 0 0 FIELD_INFO 0 0 0 1 1 0 0 1 MAX_COMP_ID 0 0 0 1 10 1 0 EXTENSION_DATA 0 0 0 1 1 0 1 1 USER_DATA 0 0 0 1 1 1 0 0DHT_MARKER 0 0 0 1 1 1 0 1 DQT_MARKER 0 0 0 1 1 1 1 0 (reserved)DNL_MARKER 0 0 0 1 1 1 1 1 (reserved) DRI_MARKER 1 1 1 0 1 0 0 0(reserved) 1 1 1 0 1 0 0 1 (reserved) 1 1 1 0 1 0 1 0 (reserved) 1 1 1 01 0 1 1 (reserved) 1 1 1 0 1 1 0 0 BIT_RATE 1 1 1 0 1 1 0 1VBV_BUFFER_SIZE 1 1 1 0 1 1 1 0 VBV_DELAY 1 1 1 0 1 1 1 1 PICTURE_TYPE 11 1 1 0 0 0 0 PICTURE_RATE 1 1 1 1 0 0 0 1 PEL_ASPECT 1 1 1 1 0 0 1 0HORIZONTAL_SIZE 1 1 1 1 0 0 1 1 VERTICAL_SIZE 1 1 1 1 0 1 0 0BROKEN_CLOSED 1 1 1 1 0 1 0 1 CONSTRAINED 1 1 1 1 0 1 1 0 (reserved)SPECTRAL_LIMIT 1 1 1 1 0 1 1 1 DEFINE_MAX_SAMPLING 1 1 1 1 1 0 0 0(reserved) 1 1 1 1 1 0 0 1 (reserved) 1 1 1 1 1 0 1 0 (reserved) 1 1 1 11 0 1 1 (reserved) 1 1 1 1 1 1 0 0 HORIZONTAL_MBS 1 1 1 1 1 1 0 1VERTICAL_MBS 1 1 1 1 1 1 1 0 (reserved) 1 1 1 1 1 1 1 1 (reserved)

[0826] A.3.4 Description of Tokens

[0827] This section documents the Tokens which are implemented in theSpatial Decoder and the Temporal Decoder chips in accordance with thepresent invention; see Table A.3.2.

[0828] Note:

[0829] “r” signifies bits that are currently reserved and carry thevalue 0

[0830] unless indicated all integers are unsigned TABLE A.3.2 Tokensimplemented in the Spatial Decoder and Temporal Decoder E 7 6 5 4 3 2 10 Description 1 1 1 1 0 1 1 0 0 BIT_RATE test info only 1 r r r r r r bb Carries the MPEG bit rate parameter P. Generated by the Huffmandecoder when decoding an MPEG bitstream. 1 b b b b b b b b b - an 18 bitinteger as defined by MPEG. 0 b b b b b b b b 1 1 1 1 1 0 1 0 0BROKEN_CLOSED 0 r r r r r r c b Carries two MPEG flag bits: c -closed_gap b - broken_link 1 0 0 0 1 0 1 0 1 CODING_STANDARD s s s s s ss s s - an 8 bit integer indicating the current coding standard. Thevalues currently assigned are: 0 - H 261 1 - JPEG 2 - MPEG 1 1 1 0 0 0 0c c COMPONENT_NAME 0 n n n n n n n n Communicates the relationshipbetween a component ID and the component name. See also... c - 2 bitcomponent ID n - 8 bit component “name” 1 1 1 1 1 0 1 0 1 CONSTRAINED 0r r r r r r r c c - carries the constrained_parameters_flag decoded froman MPEG bitstream. 1 0 0 0 0 0 1 c c DATA 1 d d d d d d d d Carries datathrough the decoder chip-set. 0 d d d d d d d d c - a 2 bit integercomponent ID (see A.3.5.1). This field is not defined for Tokens thatcarry coded data (rather than pixel information). 1 1 1 1 1 0 1 1 1DEFINE_MAX_SAMPLING 1 r r r r r r h h Max. Horizontal and Verticalsampling numbers. These describe the maximum number of blockshorizontally/vertically in any component of a macroblock. See A.3.5.2 0r r r r r r v v h - 2 bit horizontal sampling number v - 2 bit verticalsampling number 1 1 1 0 0 0 1 c c DEFINE_SAMPLING 1 r r r r r r h hHorizontal and Vertical sampling numbers for a particular colour 0 r r rr r r v v component. See A.3.5.2 c - 2 bit component ID. h - 2 bithorizontal sampling number v - 2 bit vertical sampling number. 0 0 0 0 11 1 0 0 DHT_MARKER This Token informs the Video Demux that the DATAToken that follows contains the specification of a Huffman tabledescribed using the JPEG “define Huffman table segment” syntax. ThisToken is only valid when the coding standard is configured as JPEG. ThisToken is generated by the start code detector during JPEG decoding whena DHT marker has been encountered in the data stream. 0 0 0 0 1 1 1 1 0DNL_MARKER This Token informs the Video Demux that the DATA Token thatfollows contains the JPEG parameter NL which specifies the number oflines in a frame. This Token is generated by the start code detectorduring JPEG decoding when a DNL marker has been encountered in the datastream. 0 0 0 0 1 1 1 0 1 DQT_MARKER This Token informs the Video Demuxthat the DATA Token that follows contains the specification of aquantisation table described using the JPEG “define quantisation tablesegment” syntax. This Token is only valid when the coding standard isconfigured as JPEG. The Video Demux generates a QUANT_TABLE Tokencontaining the new quantisation table information. This Token isgenerated by the start code detector during JPEG decoding when a DQTmarker has been encountered in the data stream. 0 0 0 0 1 1 1 1 1DRI_MARKER This Token informs the Video Demux that the DATA Token thatfollows contains the JPEG parameter RI which specifies the number ofminimum coding units between restart markers. This Token is generated bythe start code detector during JPEG decoding when a DRI marker has beenencountered in the data stream. 1 0 0 0 1 1 0 1 0 EXTENSION_DATA JPEG 0v v v v v v v v This Token informs the Video Demux that the DATA Tokenthat follows contains extension data. See A.11.3, “Conversion of startcodes to Tokens”, and A.14.6. “Receiving User and Extension data”,During JPEG operation the 8 bit field “V” carries the JPEG marker value.This allows the class of extension data to be identified. 0 0 0 0 1 1 01 0 EXTENSION_DATA MPEG This Token informs the Video Demux that the DATAToken that follows contains extension data. See A.11.3, “Conversion ofstart codes to Tokens”, and A.14.6. “Receiving User and Extension data”.1 0 0 0 1 1 0 0 0 FIELD_INFO 0 r r r t p t t t Carries information aboutthe picture following to aid its display. This function is not signalledby any existing coding standard. t - If the picture is an interfacedframe this bit indicates if the upper field is first (t = 0) or second.p - if pictures are fields this indicates if the next picture is upper(p = 0) or lower in the frame. 1 - a 3 bit number indicating position ofthe field in the 8 field PAL sequence. 0 0 0 0 1 0 1 1 1 FLUSH Used toindicate the end of the current coded data and to push the end of thedata stream through the decoder. 0 0 0 0 1 0 0 0 1 GROUP_START Generatedwhen the group of pictures start code is found when decoding MPEG or theframe marker is found when decoding JPEG. 1 1 1 1 1 1 1 0 0HORIZONTAL_MBS 1 r r r h h h h h h - a 13 bit number integer indicatingthe horizontal width of the 0 h h h h h h h h picture in macroblocks. 11 1 1 1 0 0 1 0 HORIZONTAL_SIZE 1 h h h h h h h h h - 16 bit numberinteger indicating the horizontal width of the 0 h h h h h h h h picturein pixels. This can be any integer value. 1 1 1 0 0 1 0 c cJPEG_TABLE_SELECT 0 r r r r r r t t Informs the inverse quantiser whichquantisation table to use on the specified colour component. c - 2 bitcomponent ID (see A.3.5.1 t - 2 bit integer table number. 1 0 0 0 1 1 00 1 MAX_COMP_ID 0 r r r r r r m m m - 2 bit integer indicating themaximum value of component ID (see A.3.5.1) that will be used in thenext picture. 0 1 1 0 1 0 1 c c MPEG_DCH_TABLE 0 r r r r r r t tConfigures which DC coefficient Huffman Lable should be used for colourcomponent cc. c - 2 bit component ID (see A.3.5.1 1 - 2 bit integertable number. 0 1 1 0 0 1 1 d n MPEG_TABLE_SELECT Informs the inversequantiser whether to use the default or user defined quantisation tablefor intra or non-intra information. n - 0 indicates intra information, 1non-intra. d - 0 indicates default table. 1 user defined. 1 1 0 1 d v vv v MVD_BACKWARDS 0 v v v v v v v v Carries one component (eithervertical or horizontal) of the backwards motion vector. d - 0 indicatesx component, 1 the y component v - 12 bit two's complement number. TheLSB provides half pixel resolution. 1 1 0 0 d v v v v MVD_FORWARDS 0 v vv v v v v v Carries one component (either vertical or horizontal) of theforwards motion vector. d - 0 indicates x component, 1 the y componentv - 12 bit two's complement number. The LSB provides half pixelresolution. 0 0 0 0 0 0 0 0 0 NULL Does nothing 1 1 1 1 1 0 0 0 1PEL_ASPECT 0 r r r r p p p p p - a 4 bit integer as defined by MPEG 0 00 0 1 0 1 1 0 PICTURE_END Inserted by the start code detector toindicate the end of the current picture. 1 1 1 1 1 0 0 0 0 PICTURE_RATE0 r r r r p p p p p - a 4 bit integer as defined by MPEG. 1 0 0 0 1 0 01 0 PICTURE_START 0 r r r r n n n n Indicates the start of a newpicture. n - a 4 bit picture index allocated to the picture by the startcode detector. 1 1 1 1 0 1 1 1 1 PICTURE_TYPE MPEG 0 r r r r r r p p p -a 2 bit integer indicating the picture coding type of the picture thatfollows: 0 - Intra 1 - Predicted 2 - Bidirectionally Predicted 3 - DCIntra 1 1 1 1 0 1 1 1 1 PICTURE_TYPE H.261 1 r r r r r r 0 1 Indicatesvarious H.261 options are on (1) or off (0). These options are alwaysoff for MPEG and JPEG: 0 r r s d f q 1 1 s - Split Screen Indicator d -Document Camera f - Freeze Picture Release Source picture format: q =0 - QCIF q = 1 - CIF 0 0 1 0 h y x b f PREDICTION_MODE A set of flagbits that indicate the prediction mode for the macroblocks that follow:f - forward prediction b - backward prediction x - reset forward vectorpredictor y - reset backward vector predictor h - enable H.261 loopfilter 0 0 0 1 s s s s s QUANT_SCALE Informs the inverse quantiser of anew scale factor s - a 5 bit integer in range 1 ..31. The value 0 isreserved. 1 0 0 0 0 1 r t t QUANT_TABLE 1 q q q q q q q q Loads thespecified inverse quantiser table with 64 8 bit unsigned integers. Thevalues are in zig-zag order 0 q q q q q q q q t - 2 bit integerspecifying the inverse quantiser table to be loaded. 0 0 0 0 1 0 1 0 0SEQUENCE_END The MPEG sequence_end_code and the JPEG EOI marker causethis Token to be generated. 0 0 0 0 1 0 0 0 0 SEQUENCE_START Generatedby the MPEG sequence_start start code. 1 0 0 0 1 0 0 1 1 SLICE_START 0 ss s s s s s s Corresponds to the MPEG slice_start, the H.261 GOB and theJPEG resync interval. The interpretation of 8 bit integer “s” differsbetween coding standards: MPEG - Slice Vertical Position - 1. H.261 -Group of blocks Number - 1. JPEG - resychronisation intervalidentification (4 LSBs only). 1 1 1 0 1 0 0 t t TEMPORAL_REFERENCE 0 t tt t t t t t t - carries the temporal reference. For MPEG this is a 10bit integer. For H.261 only the 5 LSBs are used, the MSBs will always bezero. 1 1 1 1 0 0 1 0 d TIME_CODE 1 r r r h h h h h The MPEG time_code:1 r r m m m m m m d - Drop frame flag 1 r r s s s s s s h - 5 bitinteger specifying hours 0 r r p p p p p p m - 6 bit integer specifyingminutes s - 6 bit integer specifying seconds p - 6 bit integerspecifying pictures. 1 0 0 0 1 1 0 1 1 USER_DATA JPEG 0 v v v v v v v vThis Token informs the Video Demux that the DATA Token that followscontains user data. See A.11.3, “Conversion of start codes to Tokens”,and A.14.6, “Receiving User and Extension data”. During JPEG operationthe 8 bit field carries the JPEG marker value. This allows the class ofuser data to be identified. 0 0 0 0 1 1 0 1 1 USER_DATA MPEG This Tokeninforms the Video Demux that the DATA Token that follows contains userdata. See A.11.3, “Conversion of start codes to Tokens”, and A.14.6,“Receiving User and Extension data” 1 1 1 1 0 1 1 0 1 VBV_BUFFER_SIZE 1r r r r r r s s s - a 10 bit integer as defined by MPEG 0 s s s s s s ss 1 1 1 1 0 1 1 1 0 VBV_DELAY 1 b b b b b b b b b - a 16 bit integer asdefined by MPEG 0 b b b b b b b b 1 1 1 1 1 1 1 0 1 VERTICAL_MBS 1 r r rv v v v v v - a 13 bit integer indicating the vertical size of thepicture in macroblocks 1 r r r v v v v v 1 1 1 1 1 0 0 1 1 VERTICAL_SIZE1 v v v v v v v v v - a 16 bit integer indicating the vertical size ofthe picture in pixels. 0 v v v v v v v v This can be any integer value.

[0831] A.3.5 Numbers Signalled in Tokens

[0832] A.3.5.1 Component Identification Number

[0833] In accordance with the present invention, the Component ID numberis a 2 bit integer specifying a color component. This 2 bit field istypically located as part of the Header in the DATA Token. With MPEG andH.261 the relationship is set forth in Table A.3.3. TABLE A.3.3Component ID for MPEG and H.261 Component ID MPEG or H.261 colourcomponent 0 Luminance (Y) 1 Blue difference signal (Cb/U) 2 Reddifference signal (Cr/V) 3 Never used

[0834] With JPEG the situation is more complex as JPEG does not limitthe color components that can be used. The decoder chips permit up to 4different color components in each scan. The IDs are allocatedsequentially as the specification of color components arrive at thedecoder.

[0835] A.3.5.2 Horizontal and Vertical Sampling Numbers

[0836] For each of the 4 color components, there is a specification forthe number of blocks arranged horizontally and vertically in amacroblock. This specification comprises a two bit integer which is oneless than the number of blocks.

[0837] For example, in MPEG (or H.261) with 4:2:0 chroma sampling (FIG.36) and component IDs allocated as per Table A.3.4. TABLE A.3.4 Samplingnumbers for 4:2:0/MPEG Com- Horizontal Width Vertical Height ponent IDsampling number in blocks sampling number in blocks 0 1 2 1 2 1 0 1 0 12 0 1 0 1 3 Not used Not used Not used Not used

[0838] With JPEG and 4:2:2 chroma sampling (allocation of component tocomponent ID will vary between applications. See A.3.5.1. Note: JPEGrequires a 2:1:1 structure for its macroblocks when processing 4:2:2data. See Table A.3.5. TABLE A.3.5 Sampling numbers for 4:2:2 JPEG Com-Horizontal Width Vertical Height ponent ID sampling number in blockssampling number in blocks Y 1 2 0 1 U 0 1 0 1 V 0 1 0 1

[0839] A.3.6 Special Token formats

[0840] In accordance with the present invention, tokens such as the DATAToken and the QUANT_TABLE Token are used in their “extended form” withinthe decoder chip-set. In the extended form the Token includes some data.In the case of DATA Tokens, they can contain coded data or pixel data.In the case of QUANT_TABLE tokens, they contain quantizer tableinformation.

[0841] Furthermore, “non-extended form” of these Tokens is defined inthe present invention as “empty”. This Token format provides a place inthe Token stream that can be subsequently filled by an extended versionof the same Token. This format is mainly applicable to encoders and,therefore, it is not documented further here. TABLE A.3.6 tokens fordifferent standards Token Name MPEG JPEG H.261 BIT_RATE ✓ BROKEN_CLOSED✓ CODING_STANDARD ✓ ✓ ✓ COMPONENT_NAME ✓ CONSTRAINED ✓ DATA ✓ ✓ ✓DEFINE_MAX_SAMPLING ✓ ✓ ✓ DEFINE_SAMPLING ✓ ✓ ✓ DHT_MARKER ✓ DNL_MARKER✓ DQT_MARKER ✓ DRI_MARKER ✓ EXTENSION_DATA ✓ ✓ FIELD_INFO FLUSH ✓ ✓ ✓GROUP_START ✓ ✓ HORIZONTAL_MBS ✓ ✓ ✓ HORIZONTAL_SIZE ✓ ✓ ✓JPEG_TABLE_SELECT ✓ MAX_COMP_ID ✓ ✓ ✓ MPEG_DCH_TABLE ✓ MPEG_TABLE_SELECT✓ MVD_BACKWARDS ✓ MVD_FORWARDS ✓ ✓ NULL ✓ ✓ ✓ PEL_ASPECT ✓ PICTURE_END ✓✓ ✓ PICTURE_RATE ✓ PICTURE_START ✓ ✓ ✓ PICTURE_TYPE ✓ ✓ ✓PREDICTION_MODE ✓ ✓ ✓ QUANT_SCALE ✓ ✓ QUANT_TABLE ✓ ✓ SEQUENCE_END ✓ ✓SEQUENCE_START ✓ ✓ ✓ SLICE_START ✓ ✓ ✓ TEMPORAL_REFERENCE ✓ ✓ TIME_CODE✓ USER_DATA ✓ ✓ VBV_BUFFER_SIZE ✓ VBV_DELAY ✓ VERTICAL_MBS ✓ ✓ ✓VERTICAL_SIZE ✓ ✓ ✓

[0842] A.3.7 Use of Tokens for Different Standards

[0843] Each standard uses a different sub-set of the defined Tokens inaccordance with the present invention; ss Table A.3.6.

[0844] Section A.4 The Two Wire Interface

[0845] A.4.1 Two-wire Interfaces and the Token Port

[0846] A simple two-wire valid/accept protocol is used at all levels inthe chip-set to control the flow of information. Data is onlytransferred between blocks when both the sender and receiver areobserved to be ready when the clock rises.

[0847] 1) Data transfer

[0848] 2) Receiver not ready

[0849] 3) Sender not ready

[0850] If the sender is not ready (as in 3 Sender not ready above) theinput of the receiver must wait. If the receiver is not ready (as in 2Receiver not ready above) the sender will continue to present the samedata on its output until it is accepted by the receiver. When Tokeninformation is transferred between blocks the two-wire interface betweenthe blocks is referred to as a Token Port.

[0851] A.4.2 Where Used

[0852] The decoder chip-set, in accordance with the present invention,uses two-wire interfaces to connect the three chips. In addition, thecoded data input to the Spatial Decoder is also a two-wire interface.

[0853] A.4.3 Bus Signals

[0854] The width of the data word transferred by the two-wire interfacevaries depending upon the needs of the interface concerned (See FIG. 35,“Tokens on interfaces wider than 8 bits”. For example, 12 bitcoefficients are input to the Inverse Discrete Cosine Transform (IDCT),but only 9 bits are output. TABLE A.4.1 Two wire interface data widthInterface Data Width (bits) Coded data input to Spatial Decoder 8 Outputport of Spatial Decoder 9 Input port of Temporal Decoder 9 Output portof Temporal Decoder 8 Input port of Image Formatter 8

[0855] In addition to the data signals there are three other signalstransmitted via the two-wire interface:

[0856] valid

[0857] accept

[0858] extension

[0859] A.4.3.1 The Extension Signal

[0860] The extension signal corresponds to the Token extension bitpreviously described.

[0861] A.4.4 Design Considerations

[0862] The two wire interface is intended for short range, point topoint communication between chips.

[0863] The decoder chips should be placed adjacent to each other, so asto minimize the length of the PCB tracks between chips. Where possible,track lengths should be kept below 25 mm. The PCB track capacitanceshould be kept to a minimum.

[0864] The clock distribution should be designed to minimize the clockslew between chips. If there is any clock slew, it should be arranged sothat “receiving chips” see the clock before “sending chips”.¹

[0865] All chips communicating via two wire interfaces should operatefrom the same digital power supply.

[0866] A.4.5 Interface Timing TABLE A.4.2 Two wire interface timing 30MHz Num. Characterstic Min. Max. Unit Note^(a b) 1 Input signal set-uptime 5 ns 2 Input signal hold time 0 ns 3 Output signal drive time 23 ns4 OutPut signal hold time 2 ns

[0867] A.4.6 Signal Levels

[0868] The two-wire interface uses CMOS inputs anti output. V_(1Hmin) isapprox. 70% of V_(DD) and V_(1max) is approx. 30% of V_(DD). The valuesshown in Table A.4.3 are those for V_(1H) and V_(1L) at their respectiveworst case V_(DD). V_(DD)=5.0∀0.25V. TABLE A.4.3 DC electricalcharacteristics Symbol Parameter Min. Max. Units V_(1H) Input logic ‘1’voltage 3.68 V_(DD) − 0.5 V V_(1L) Input logic ‘0’ voltage GND − 0.51.43 V V_(OH) Output logic ‘1’ voltage V_(DD) − 0.1 V^(a) V_(DD) − 0.4V^(b) V_(OL) Output logic ‘0’ voltage 0.1 V^(c) 0.4 V^(d) I_(IN) Inputleakage current ±10 ΦA

[0869] A.4.7 Control Clock

[0870] In general, the clock controlling the transfers across the twowire interface is the chip's decoder_clock. The exception is the codeddata port input to the Spatial Decoder. This is controlled bycoded_clock. The clock signals are further described herein.

[0871] Section A.5 DRAM Interface

[0872] A.S.1 The DRAM Interface

[0873] A single high performance, configurable, DRAM interface is usedon each of the video decoder chips. In general, the DRAM interface oneach chip is substantially the same; however, the interfaces differ fromone another in how they handle channel priorities. The interface isdesigned to directly drive the DRAM used by each of the decoder chips.Typically, no external logic, buffers or components will be necessary toconnect the DRAM interface to the DRAMs in most systems.

[0874] A.5.2 Interface Signals TABLE A.5.1 DRAM interface signals Input/Signal Name Output Description DRAM_data[31:0] I/O The 32 bit wide DRAMdata bus. Optionally this bus can be configured to be 16 or 8 bits wide.See section A.5.8 DRAM_addr[10:0] O The 22 bit wide DRAM interfaceaddress is time multiplexed over this 11 bit wide bus. {overscore (RAS)}O The DRAM Row Address Strobe signal {overscore (CAS)}[3:0] O The DRAMColumn Address Strobe signal. One signal is provided per byte of theinterface's data bus. All the {overscore (CAS)} signals are drivensimultaneously. {overscore (WE)} O The DRAM Write Enable signal{overscore (OE)} O The DRAM Output Enable signal DRAM_enable I Thisinput signal, when low, makes all the output signals on the interface gohigh impedance. Note: on-chip data processing is not stopped when theDRAM interface is high impedance. So, errors will occur if the chipattempts to access DRAM while DRAM_enable is low.

[0875] In accordance with the present invention, the interface isconfigurable in two ways:

[0876] The detail timing of the interface can be configured toaccommodate a variety of different DRAM types

[0877] The “width” of the DRAM interface can be configured to provide acost/performance trade-off in different applications.

[0878] A.5.3 Configuring the DRAM Interface

[0879] Generally, there are three groups of registers associated withthe DRAM interface: interface timing configuration registers, interfacebus configuration registers and refresh configuration registers. Therefresh configuration registers (registers in Table A.5.4) should beconfigured last.

[0880] A.5.3.1 Conditions After Reset

[0881] After reset, the DRAM interface, in accordance with the presentinvention, starts operation with a set of default timing parameters(that correspond to the slowest mode of operation). Initially, the DRAMinterface will continually execute refresh cycles (excluding all othertransfers). This will continue until a value is written intorefresh_interval. The DRAM interface will then be able to perform othertypes of transfer between refresh cycles.

[0882] A.5.3.2 Bus Configuration

[0883] Bus configuration (registers in Table A.5.3) should only be donewhen no data transfers are being attempted by the interface. Theinterface is placed in this condition immediately after reset, andbefore a value is written into refresh_interval. The interface can bere-configured later, if required, only when no transfers are beingattempted. See the Temporal Decoder chip_access register (A.13.3.1) andthe Spatial Decoder buffer_manager_access register (A.13.1.1).

[0884] A.5.3.Interface Timing Configuration

[0885] In accordance with the present invention, modifications to theinterface timing configuration information are controlled by theinterface_timing_access register. Writing 1 to this register allows theinterface timing registers (in Table A.5.2) to be modified. Whileinterface_timing_access=1, the DRAM interface continues operation withits previous configuration. After writing 1, the user should wait until1 can be read back from the interface_timing_access before writing toany of the interface timing registers. When configuration is compete, 0should be written to the interface_timing_access. The new configurationwill then be transferred to the DRAM interface.

[0886] A.5.3.4 Refresh Configuration

[0887] The refresh interval of the DRAM interface of the presentinvention can only be configured once following reset. Untilrefresh_interval is configured, the interface continually executesrefresh cycles. This prevents any other data transfers. Data transferscan start after a value is written to refresh_interval.

[0888] As is well known in the art, DRAMs typically require a “pause” ofbetween 100 μs and 500 μs after power is first applied, followed by anumber of refresh cycles before normal operation is possible.Accordingly, these DRAM start-up requirements should be satisfied beforewriting a value to refresh_interval.

[0889] A.5.3.5 Read Access to Configuration Registers

[0890] All the DRAM interface registers of the present invention can beread at any time.

[0891] A.5.4 Interface Timing (Ticks)

[0892] The DRAM interface timing is derived from a Clock which isrunning at four times the input Clock rate of the device(decoder_clock). This clock is generated by an on-chip PLL.

[0893] For brevity, periods of this high speed clock are referred to asticks.

[0894] A. 5.5 Interface Registers TABLE A.5.2 Interface timingconfiguration registers Size/ Reset Register name Dir. State Descriptioninterface_timing_access 1 0 This function enable register bit allowsaccess to the DRAM rw interface timing configuration registers. Theconfiguration registers should not be modified while this register holdsthe value 0. Writing a one to this register requests access to modifythe configuration registers. After a 0 has been written to this registerthe DRAM interface will start to use the new values in the timingconfiguration registers. page_start_length 5 0 Specifies the length ofthe bit access start in ticks. rw The minimum value that can be used is4 (meaning 4 ticks). 0 selects the maximum length of 32 ticks.transfer_cycle_length 4 0 Specifies the length of the fast bit page reador write cycle in ticks. rw The minimum value that can be used is 4(meaning 4 ticks). 0 selects the maximum length of 16 ticks.refresh_cycle_length 4 0 Specifies the length of the bit refresh cyclein ticks. The rw minimum value that can be used is 4 (meaning 4 ticks).0 selects the maximum length of 16 ticks. RAS_falling 4 0 Specifies thenumber of ticks bit after the start of the access start rw that{overscore (RAS)} falls. The minimum value that can be used is 4(meaning 4 ticks). 0 selects the maximum length of 16 ticks. CAS_falling4 8 Specifies the number of ticks bit after the start of a read cycle,rw write cycle or access start that {overscore (CAS)} falls. The minimumvalue that can be used is 1 (meaning 1 tick). 0 selects the maximumlength of 16 ticks.

[0895] TABLE A.5.3 Interface bus configuration registers State/ ResetRegister name Dir. State Description DRAM_data_width 2 0 Specifies thenumber of bits bit used on the DRAM interface rw data busDRAM_data[31:0]. See A.5.8 row_address_bits 2 0 Specifies the number ofbits bit used for the row address portion rw of the DRAM interfaceaddress bus. See A.5.10 DRAM_enable 1 1 Writing the value 0 in to thisbit register forces the DRAM rw interface into a high impedance state. 0will be read from this register if either the DRAM_enable signal is lowor 0 has been written to the register. CAS_strength 3 6 These three bitregisters RAS_strength bit configure the output drive addr_strength rwstrength of DRAM interface DRAM_data_strength signals. This allows theinterface OEWE_strength to be configured for various different loads.See A.5.13

[0896] A.5.6 Interface Operation

[0897] The DRAM interface uses fast page mode. Three different types ofaccess are supported:

[0898] Read

[0899] Write

[0900] Refresh

[0901] Each read or write access transfers a burst of 1 to 64 bytes to asingle DRAM page address. Read and write transfers are not mixed withina single access and each successive access is treated as a random accessto a new DRAM page. TABLE A.5.4 Refresh configuration registers Size/Reset Register name Dir. State Description refresh_interval 8 0 Thisvalue specifies the interval bit between refresh cycles in periods of 16rw decoder_clock cycles. Values in the range 1 . . . 255 can beconfigured. The value 0 is automatically loaded after reset and forcesthe DRAM interface to continuously execute refresh cycles until a validrefresh interval is configured. It is recommended that refresh_intervalshould be configured only once after each reset. no_refresh 1 0 Writingthe value 1 to this register pre- bit vents execution of any refreshcycles. rw

[0902] A.5.7 Access Structure

[0903] Each access is composed of two parts:

[0904] Access start

[0905] Data transfer

[0906] In the present invention, each access begins with an access startand is followed by one or more data transfer cycles. In addition, thereis a read, write and refresh variant of both the access start and thedata transfer cycle.

[0907] Upon completion of the last data transfer for a particularaccess, the interface enters its default state (see A.5.7.3) and remainsin this state until a new access is ready to begin. If a new access isready to begin when the last access has finished, then the new accesswill begin immediately.

[0908] A.5.7.1 Access Start

[0909] The access start provides the page address for the read or writetransfers and establishes some initial signal conditions. In accordancewith the present invention, there are three different access starts:

[0910] Start of read

[0911] Start of write

[0912] Start of refresh TABLE A.5.5 DRAM Interface timing parametersNum. Characteristic Min. Max. Unit Notes 5 {overscore (RAS)} prechargeperiod set by register 4 16 DCK RAS_falling 6 Access start duration setby register 4 32 page_start_length 7 {overscore (CAS)} percharge lengthset by register 1 16 ^(a) CAS_falling 8 Fast page read or write cyclelength 4 16 set by the register transfer_cycle_length. 9 Refresh cyclelength set by the 4 16 register refresh_cycle.

[0913] In each case, the timing of RAS and the row address is controlledby the registers RAS_falling and page start length. The state of OE andDRAM_data[31:0] is held from the end of the previous data transfer until**RAS falls. The three different access start types only vary in howthey drive OE and DRAM_data[31:0] when RAS falls. See FIG. 43.

[0914] A.5.7.2 Data Transfer

[0915] In the present invention, there are different types of datatransfer cycles:

[0916] Fast page read cycle

[0917] Fast page late write cycle

[0918] Refresh cycle

[0919] A start of refresh can only be followed by a single refreshcycle. A start of read (or write) can be followed by one or more fastpage read (or write) cycles. At the start of the read cycle CAS isdriven high and the new column address is driven.

[0920] Furthermore, an early write cycle is used. WE is driven low atthe start of the first write transfer and remains low until the end ofthe last write transfer. The output data is driven with the address.

[0921] As a CAS before RAS refresh cycle is initiated by the start ofrefresh cycle, there is no interface signal activity during the refreshcycle. The purpose of the refresh cycle is to meet the minimum RAS lowperiod required by the DRAM.

[0922] A.5.7.3 Interface Default State

[0923] The interface signals in the present invention enter a defaultstate at the end-of an access: RAS, CAS and WE high

[0924] data and OE remain in their previous state

[0925] addr remains stable

[0926] A.5.8 Data Bus Width

[0927] The two bit register, DRAM_data_width, allows the width of theDRAM interface's data path to be configured. This allows the DRAM costto be minimized when working with small picture formats. TABLE A.5.6Configuring DRAM_data_width DRAM_data_width 0^(a) 8 bit wide data bus onDRAM_data(31:24)^(a). 1 16 bit wide data bus on DRAM_data(31:16)^(b). 232 bit wide data bus on DRAM_data(31:0).

[0928] A.5.9 Row Address Width

[0929] The number of bits that are taken from the middle section of the24 bit internal address in order to provide the row address isconfigured by the register, row_address_bits. TABLE A.5.7 Configuringrow_address_bits row_address_bits Width of row address 1 10 bits onDRAM_addr(9:0) 2 11 bits on DRAM_addr(10:0)

[0930] A.5.10 Address Bits

[0931] On-chip, a 24 bit address is generated. How this address is usedto form the row and column addresses depends on the width of the databus and the number of bits selected for the row address. Someconfigurations do not permit all the internal address bits to be usedand, therefore, produce “hidden bits)”.

[0932] Similarly, the row address is extracted from the middle portionof the address. Accordingly, this maximizes the rate at which the DRAMis naturally refreshed. TABLE A.5.8 Mapping between internal andexternal addresses row row address data address translation bus columnaddress translation width internal

external width internal

external 9 (14:6)

(8:0) 8 (19:15)

(10:6) (5:0)

(5:0) 16 (20:15)

(10:5) (5:1)

(4:0) 32 (21:15)

(10:4) (5:2)

(3:0) 10 (15:6)

(9:0) 8 (19:16)

(10:6) (5:0)

(5:0) 16 (20:16)

(10:5) (5:1)

(4:0) 32 (21:16)

(10:4) (5:2)

(3:0) 11  (16:6)

(10:0) 8 (19:17)

(10:6) (5:0)

(5:0) 16 (20:17)

(10:5) (5:1)

(4:0) 32 (21:17)

(10:4) (5:2)

(3:0)

[0933] A.5.10.1 Low Order Column Address Bits

[0934] The least significant 4 to 6 bits of the column address are usedto provide addresses for fast page mode transfers of up to 64 bytes. Thenumber of address bits required to control these transfers will dependon the width of the data bus (see A.5.8).

[0935] A.5.10.2 Decoding Row Address to Access more DRAM Banks

[0936] Where only a single bank of DRAM is used, the width of the rowaddress used will depend on the type of DRAM used. Applications thatrequire more memory than can be typically provided by a single DRAMbank, can configure a wider row address and then decode some row addressbits to select a single DRAM bank.

[0937] NOTE: The row address is extracted from the middle of theinternal address. If some bits of the row address are decoded to selectbanks of DRAM, then all possible values of these “bank select bits” mustselect a bank of DRAM. Otherwise, holes will be left in the addressspace.

[0938] A.5.11 DRAM Interface Enable

[0939] In the present invention, there are two ways to make all theoutput signals on the DRAM interface become high impedance, i.e., bysetting the DRAM enable register and the DRAM-enable signal. Both theregister and the signal must be at a logic 1 in order for the drivers onthe DRAM interface to operate. If either is low then the interface istaken to high impedance.

[0940] Note: on-chip data processing is not terminated when the DRAMinterface is at high impedance. Therefore, errors will occur if the chipattempts to access DRAM while the interface is at high impedance.

[0941] In accordance with the present invention, the ability to take theDRAM interface to high impedance is provided to allow other devices totest or use the DRAM controlled by the Spatial Decoder (or the TemporalDecoder) when the Spatial Decoder (or the Temporal Decoder) is not inuse. It is not intended to allow other devices to share the memoryduring normal operation.

[0942] A.5.12 Refresh

[0943] Unless disabled by writing to the register, no_refresh, the DRAMinterface will automatically refresh the DRAM using a {overscore (CAS)}before {overscore (RAS)} refresh cycle at an interval determined by theregister, refresh_interval.

[0944] The value in refresh_interval specifies the interval betweenrefresh cycles in periods of 16 decoder_clock cycles. Values in therange 1.255 can be configured. The value 0 is automatically loaded afterreset and forces the DRAM interface to continuously execute refreshcycles (once enabled) until a valid refresh interval is configured. Itis recommended that refresh_interval should be configured only onceafter each reset.

[0945] While {overscore (reset)} is asserted, the DRAM interface isunable to refresh the DRAM. However, the reset time required by thedecoder chips is sufficiently short, so that it should be possible toreset them and then to re-configure the DRAM interface before the DRAMcontents decay.

[0946] A.5.13 Signal Strengths

[0947] The drive strength of the outputs of the DRAM interface can beconfigured by the user using the 3 bit registers, CAS_strength,RAS_strength, addr_strength, DRAM_data_strength, and OEWE_strength. TheMSB of this 3 bit value selects either a fast or slow edge rate. The twoless significant bits configure the output for different loadcapacitances.

[0948] The default strength after reset is 6 and this configures theoutputs to take approximately Ions to drive a signal between GND andV_(DD) if loaded with 24_(P)F. TABLE A.5.9 Output strengthconfigurations strength value Drive characteristics 0 Approx. 4 ns/Vinto 6 pf load 1 Approx. 4 ns/V into 12 pf load 2 Approx. 4 ns/V into 24pf load 3 Approx. 4 ns/V into 48 pf load 4 Approx. 2 ns/V into 6 pf load5 Approx. 2 ns/V into 12 pf load 6^(a) Approx. 2 ns/V into 24 pf load 7Approx. 2 ns/V into 48 pf load

[0949] When an output is configured appropriately for the load it isdriving, it will meet the AC electrical characteristics specified inTables A.5.13 to A.5.16. When appropriately configured, each output isapproximately matched to its load and, therefore, minimal overshoot willoccur after a signal transition.

[0950] A.5.14 Electrical Specifications

[0951] All information provided in this section is merely illustrativeof one embodiment of the present invention and is included by exampleand not necessarily by way of limitation. TABLE A.5.10 MaximumRatings^(a) Symbol Parameter Min. Max. Units V_(DD) Supply voltagerelative to −0.5 6.5 V GND V_(IN) Input voltage on any pin GND − 0.5V_(DD) + 0.5 V T_(A) Operating temperature −40 +85 ° C. T_(S) Storagetemperature −55 +150 ° C.

[0952] Table A.5.10 sets forth maximum ratings for the illustrativeembodiment only. For this particular embodiment stresses below thoselisted in this table should be used to ensure reliability of operation.TABLE A.5.11 DC Operating conditions Symbol Parameter Min. Max. UnitsV_(DD) Supply voltage relative to 4.75 5.25 V GND GND Ground 0 0 VV_(IH) Input logic ‘1’ voltage 2.0 V_(DD) + 0.5 V V_(IL) Input logic ‘0’voltage GND − 0.5 0.8 V T_(A) Operating temperature 0 70 ° C.^(a)

[0953] TABLE A.5.12 DC Electrical characteristics Symbol Parameter Min.Max. Units V_(OL) Output logic ‘0’ voltage 0.4 V^(a) V_(OH) Output logic‘1’ voltage 2.8 V I_(O) Output current ±100 μA^(b) I_(OZ) Output offstate leakage current ±20 μA I_(IZ) Input leakage current ±10 μA I_(DD)RMS power supply current 500 mA C_(IN) Input capacitance 5 pF C_(OUT)Output/IO capacitance 5 pF

[0954] A.5.14.1 AC Characteristics TABLE A.5.13 Differences from nominalvalues for a strobe Num. Parameter Min. Max. Unit Note^(a) 10 Cycle time−2 +2 ns 11 Cycle time −2 +2 ns 12 High pulse −5 +2 ns 13 Low pulse −11+2 ns 14 Cycle time −8 +2 ns

[0955] TABLE A.5.14 Differences from nominal values between two strobesNum. Parameter Min. Max. Unit Note^(a) 15 Strobe to strobe delay −3 +3ns 16 Low hold time −13 +3 ns 17 Strobe to strobe precharge e.g. tCRP,−9 +3 ns tRCS, tRCH, tRRH, tRPC {overscore (CAS)} precharge pulsebetween any −5 +2 ns two {overscore (CAS)} signals on wide DRAMs e.g.tCP, or between {overscore (RAS)} rising and {overscore (CAS)} fallinge.g. tRPC 18 Precharge before disable −12 +3 ns

[0956] TABLE A.5.15 Differences from nominal between a bus and a strobeNum. Parameter Min. Max. Unit Note^(a) 19 Set up time −12 +3 ns 20 Holdtime −12 +3 ns 21 Address access time −12 +3 ns 22 Next valid afterstrobe −12 +3 ns

[0957] TABLE A.5.16 Differences from nominal between a bus and a strobeNum. Parameter Min. Max. Unit Note 23 Read data set-up time before{overscore (CAS)} 0 ns signal starts to rise 24 Read data hold timeafter {overscore (CAS)} signal 0 ns starts to go high

[0958] When reading from DRAM, the DRAM interface samplesDRAM_data[31:0] as the {overscore (CAS)} signals rise. TABLE A.5.17Cross-reference between “standard” DRAM parameter names and timingparameter numbers parameter name number tPC 10 tRC 11 tRP 12 tCP tCPNtRAS 13 tCAS tCAC tWP tRASP tRASC tACP/tCPA 14 tRCD 15 tCSR tRSH 16 tCSHtRWL tCWL tRAC tOAC/tOE tCHR tCRP 17 tRCS tRCH tRRH tRPC tCP tRPC tRHCP18 tCPRH tASR 19 tASC tDS tRAH 20 tCAH tDH tAR tAA 21 tRAL tRAD 22

[0959] Section A.6 Microprocessor Interface (MPI)

[0960] A standard byte wide microprocessor interface (MPI) is used onall chips in the video decoder chip-set. However, one of ordinary skillin the art will appreciate that microprocessor interfaces of otherwidths may also be used. The MPI operates synchronously to variousdecoder chip clocks.

[0961] A.6.1 MPI Signals TABLE A.6.1 MPI interface signals Input/ SignalName Output Description {overscore (enable(1:0))} Input Two active lowchip enables. Both must be low to enable accesses via the MPI.r{overscore (w)} Input High indicates that a device wishes to readvalues from the video chip. This signal should be stable while the chipis enabled. addr(n:0) Input Address specifies one of 2^(n) locations intne chip's memory map. This signal should be stable while the chip isenabled. data(7:0) Output 8 bit wide data I/O port. These pins are highimpedance it either enable signal is high. {overscore (irq)} Output Anactive low, open collector. interrupt request signal.

[0962] A.6.2 MRI Electrical Specifications TABLE A.6.2 Absolute MaximumRatings^(a) Symbol Parameter Min. Max. Units V_(DD) Supply voltagerelative to −0.5 6.5 V GND V_(IN) Input voltage on any pin GND − 0.5V_(DD) + 0.5 V T_(A) Operating temperature −40 +85 *C T_(S) Storagetemperature −55 +150 *C

[0963] TABLE A.6.3 DC Operating conditions Symbol Parameter Min. Max.Units V_(DD) Supply voltage relative to 4.75 5.25 V GND GND Ground 0 0 VV_(IH) Input logic ‘1’ voltage 2.0 V_(DD) + 0.5 V^(a) V_(IL) Input logic‘0’ voltage GND − 0.5 0.8 V^((a)) T_(A) Operating temperature 0 70*C^(b)

[0964] TABLE A.6.4 DC Electrical characteristics Symbol Parameter Min.Max. Units V_(OL) Output logic ‘0’ voltage 0.4 V V_(OL∝) Open collectoroutput logic ‘0’ voltage 0.4 V^(a) V_(OH) Output logic ‘1’ voltage 2.4 VI_(O) Output current ±100 μA^(b) I_(O∝) Open collector output current4.0 8.0 mA^(c) I_(OZ) Output off state leakage current ±20 μA I_(IN)Input leakage current ±10 μA I_(DD) RMS power supply current 500 mAC_(IN) Input capacitance 5 pF C_(OUT) Output/IO capacitance 5 pF

[0965] A.6.2.1 AC Characteristics TABLE A.6.5 Microprocessor interfaceread timing Num. Characteristic Min. Max. Unit Notes^(a) 25 Enable lowperiod 100 ns 26 Enable high period 50 ns 27 Address or r{overscore (w)}set-up to chip 0 ns enable 28 Address or r{overscore (w)} hold from chip0 ns disable 29 Output turn-on time 20 ns 30 Read data access time 70 ns^(b) 31 Read data hold time 5 ns 32 Read data turn-off time 20

[0966] TABLE A.6.6 Microprocessor interface write timing Num.Characteristic Min. Max. Unit Notes 33 Write data set-up time 15 ns ^(a)34 Write data hold time  0 ns

[0967] A.6.3 Interrupts

[0968] In accordance with the present invention, “event” is the termused to describe an on-chip condition that a user might want to observe.An event can indicate an error or it can be informative to the user'ssoftware.

[0969] There are two single bit registers associated with each interruptor “event”. These are the condition event register and the conditionmask register.

[0970] A.6.3.1 condition Event Register

[0971] The condition event register is a one bit read/write registerwhose value is set to one by a condition occurring within the circuit.The register is set to one even if the condition was merely transientand has now gone away. The register is then guaranteed to remain set toone until the user's software resets it (or the entire chip is reset).

[0972] The register is set to zero by writing the value one

[0973] Writing zero to the register leaves the register unaltered.

[0974] The register must be set to zero by user software before anotheroccurrence of this condition can be observed.

[0975] The register will be reset to zero on reset.

[0976] A.6.3.2 Condition Mask Register

[0977] The condition mask register is one bit read/write register whichenables the generation of an interrupt request if the correspondingcondition event register(s) is (are) set. If the condition event isalready set when 1 is written to the condition mask register, aninterrupt request will be issued immediately.

[0978] The value 1 enables interrupts.

[0979] The register clears to zero on reset.

[0980] Unless stated otherwise a block will stop operation afterGenerating an interrupt request and will re-start operation after eitherthe condition event or the condition mask register is cleared. A.6.3.3Event and mask bits

[0981] Event bits and mask bits are always grouped into correspondingbit positions in consecutive bytes in the memory map (see Table A.9.6and Table A.17.6). This allows interrupt service software to use thevalue read from the mask registers as a mask for the value in the eventregisters to identify which event generated the interrupt.

[0982] A.6.3.4 The Chip Event and Mask

[0983] Each chip has a single “global” event bit that summarizes theevent activity on the chip. The chip event register presents the OR ofall the on-chip events that have 1 in their mask bit.

[0984] A 1 in the chip mask bit allows the chip to generate interrupts.A 0 in the chip mask bit prevents any on-chip events from generatinginterrupt requests.

[0985] Writing 1 to 0 to the chip event has no effect. It will onlyclear when all the events (enabled by a I in their mask bit) have beencleared.

[0986] A.6.3.5 The Irq Signal

[0987] The {overscore (irq)} signal is asserted if both the chip eventbit and the chip event mask are set.

[0988] The {overscore (irq)} signal is an active low, “open collector”output which requires an off-chip pull-up resistor. When active the{overscore (irq)} output is pulled down by an impedance of loon or less.

[0989] I will be appreciated that pull-up resistor of approximately 4 kΩshould be suitable for most applications.

[0990] A.6.4 Accessing Registers

[0991] A.6.4.1 Stopping Circuits to Enable Access

[0992] In the present invention, most registers can only modified if theblock with which they are associated is stopped. Therefore, groups ofregisters will normally be associated with an access register.

[0993] The value 0 in an access register indicates that the group ofregisters associated with that access register should not be modified.Writing 1 to an access register requests that a block be stopped.However, the block may not stop immediately and block's access registerwill hold the value 0 until it is stopped.

[0994] Accordingly, user software should wait (after writing 1 torequest access) until 1 is read from the access register. If the userwrites a value to a configuration register while its access register isset to 0, the results are undefined.

[0995] A.6.4.2 Registers Holding Integers

[0996] The least significant bit of any byte in the memory map is thatassociated with the signal data[0].

[0997] Registers that hold integers values greater than 8 bits are splitover either 2 or 4 consecutive byte locations in the memory map. Thebyte ordering is “big endian” as shown in FIG. 55. However, noassumptions are made about the order in which bytes are written intomulti-byte registers.

[0998] Unused bits in the memory map will return a 0 when read exceptfor unused bits in registers holding signed integers. In this case, themost significant bit of the register will be sign extended. For example,a 12 bit signed register will be sign extended to fill a 16 bit memorymap location (two bytes). A 16 bit memory map location holding a 12 bitunsigned integer will return a 0 from its most significant bits.

[0999] A.6.4.3 Keyholed Address Locations

[1000] In the present invention, certain less frequently accessed memorymap locations have been placed behind “keyholes”. A “keyhole” hastwo-registers associated with it, a keyhole address register and akeyhole data register.

[1001] The keyhole address specifies a location within an extendedaddress space. A read or a write operation to the keyhole data registeraccesses the-location specified by the keyhole address register.

[1002] After accessing a keyhole data register the associated keyholeaddress register increments. Random access within the extended addressspace is only possible by writing a new value to the keyhole addressregister for each access.

[1003] A chip in accordance with the present invention, may have morethan one “keyholed” memory map. There is no interaction between thedifferent keyholes.

[1004] A.6.5 Special Registers

[1005] A.6.5.1 Unused Registers

[1006] Registers or bits described as “not used” are locations in thememory map that have not been used in the current implementation of thedevice. In general, the value 0 can be read from these locations.Writing 0 to these locations will have no effect.

[1007] As will be appreciated by one of ordinary skill in the art, inorder to maintain compatibility with future A variants of theseproducts, it is recommended that the user's software should not dependupon values read from the unused locations. Similarly, when configuringthe device, these locations should either be avoided or set to the value0.

[1008] A.6.5.2 Reserved Registers

[1009] Similarly, registers or bits described as “reserved” in thepresent invention have un-documented effects on the behavior of thedevice and should not be accessed.

[1010] A.6.5.3 Test Registers

[1011] Furthermore, registers or bits described as “test registers”control various aspects of the device's testability. Therefore, theseregisters have no application in the normal use of the devices and neednot be accessed by normal device configuration and control software.

[1012] Section A.7 Clocks

[1013] In accordance with the present inventions, many different clockscan be identified in the video decoder system. Examples of clocks areillustrated in FIG. 56.

[1014] As data passes between different clock regimes within the videodecoder chip-set, it is resynchronized (on-chip) to each new clock. Inthe present invention, the maximum frequency of any input clock is 30MH_(z). However, one of ordinary skill in the art will appreciate thatother frequencies, including those greater than 30 MHz, may also beused. On each chip, the microprocessor interface (MPI) operatesasynchronously to the chip clocks. In addition, the Image Formatter cangenerate a low frequency audio clock which is synchronous to the decodedvideo's picture rate. Accordingly, this clock can be used to provideaudio/video synchronization.

[1015] A.7.1 Spatial Decoder Clock Signals

[1016] The Spatial Decoder has two different (and potentiallyasynchronous) clock inputs: TABLE A.7.1 Spatial Decoder clocks Input/Signal Name Output Description coded_clock Input This clock controlsdata transfer in to the coded data port at the Spatial Decoder. On-chipthis clock controls tne processing of the coded data until it reachesthe coded data buffer. decoder_clock Input The decoder clock controlsthe majority of the processing functions on tne Spatial Decoder. Thedecoder clock also controls the transfer at data out of the SpatialDecoder through its outout port.

[1017] A.7.2 Temporal Decoder Clock Signals

[1018] The Temporal Decoder has only one clock input: TABLE A.7.2Temporal Decoder clocks Input/ Signal Name Output Descriptiondecoder_clock Input The decoder clock controls all of the processingfunctions on the Temporal Decoder. The decoder clock also controlstransfer of data in to the Temporal Decoder through its input port andout via its output port.

[1019] A.7.3 Electrical Specifications TABLE A.7.3 Input clockrequirements 30 MHz Num. Characteristic Min. Max. Unit Note 35 Clockperiod 33 ns 36 Clock high period 13 ns 37 Clock low period 13 ns

[1020] TABLE A.7.4 Clock input conditions Symbol Parameter Min. Max.Units V_(IH) Input logic ‘2’ voltage 3.68 V_(DD) + 0.5 V V_(IL) Inputlogic ‘0’ voltage GND − 0.5 1.43 V I_(OZ) Input leakage current ±10 μA

[1021] A.7.3.1 CMOS Levels

[1022] The clock input signals are CMOS inputs. V_(1Hmin) is approx. 70%of V_(DD) and V_(1Lmax) is approx. 30% of V_(DD). The values shown inTable A.7.4 are those for V_(1L) and V_(1L) at their respective worstcase V_(DD). V_(DD)=5.0±0.25V.

[1023] A.7.3.2 Stability of Clocks

[1024] In the present invention, clocks used to drive the DRAM interfaceand the chip-to-chip interfaces are derived from the input clocksignals. The timing specifications for these interfaces assume that theinput clock timing is stable to within ±100 ps.

[1025] Section A.8 JTAG

[1026] As circuit boards become more densely populated, it isincreasingly difficult to verify the connections between components bytraditional means, such as in-circuit testing using a bed-of-nailsapproach. In an attempt to resolve the access problem and standardize ona methodology, the Joint Test Action Group (JTAG) was formed. The workof this group culminated in the “Standard Test Access Port and BoundaryScan Architecture”, now adopted by the IEEE as standard 1149.1. TheSpatial Decoder and Temporal Decoder comply with this standard.

[1027] The standard utilizes a boundary scan chain which seriallyconnects each digital signal pin on the device. The test circuitry istransparent in normal operation, but in test mode the boundary scanchain allows test patterns to be shifted in, and applied to the pins ofthe device. The resultant signals appearing on the circuit board at theinputs to the JTAG device, may be scanned out and checked by relativelysimple test equipment. By this means, the inter-component connectionscan be tested, as can areas of logic on the circuit board.

[1028] All JTAG operations are performed via the Test Access Port (TAP),which consists of five pins. The trst (Test Reset) pin resets the JTAGcircuitry, to ensure that the device doesn't power-up in test mode. Thetck (Test Clock) pin is used to clock serial test patterns into the tdi(Test Data Input) pin, and out of the tdo (Test Data Output) pin.Lastly, the operational mode of the JTAG circuitry is set by clockingthe appropriate sequence of bits into the tms (Test Mode Select) pin.

[1029] The JTAG standard is extensible to provide for additionalfeatures at the discretion of the chip manufacturer. On the SpatialDecoder and Temporal Decoder, there are 9 user instructions, includingthree JTAG mandatory instructions. The extra instructions allow a degreeof internal device testing to be performed, and provide additionalexternal test flexibility. For example, all device outputs may be madeto float by a simple JTAG sequence.

[1030] For full details of the facilities available and instructions onhow to use the JTAG port, refer to the following JTAG ApplicationsNotes.

[1031] A.8.1 Connection of JTAG Pins in Non-JTAG Systems TABLE A.8.1 Howto connect JTAG inputs Signal Direction Description {overscore (trst)}Input This pin has an internal pull-up, but must be taken low atpower-up even if the JTAG features are not being used. This may beachieved by connecting {overscore (trst)} in common with the chip resetpin {overscore (reset)}. tdi Input These pins have internal pull-ups,and may be left tms disconnected if the JTAG circuitry is not beingused. tck Input This pin does not have a pull-up, and should be tied toground if the JTAG circuitry is not used. tdo Output High impedanceexcept during JTAG scan operations. If JTAG is not being used, this pinmay be left disconnected.

[1032] A.8.2 Level of Conformance to IEEE 1149.1

[1033] A.8.2.1 Rules

[1034] All rules are adhered to, although the following should be noted:TABLE A.8.2 JTAG Rules Rules Description 3.1.1(b) The {overscore (trst)}pin is provided. 3.5.1(b) Guaranteed for all public instructions (seeIEEE 1149.1 5.2.1(c)). 5.2.1(c) Guaranteed for all public instructions.For some private instructions, the TDO pin may be active during any ofthe states Capture-DR, Exit1-DR, Exit-2-DR & Pause-DR. 5.3.1(a) Poweron-reset is achieved by use of the {overscore (trst)} pin. 6.2.1(e,f) Acode for the BYPASS instruction is loaded in the Test-Logic-Reset state.7.1.1(d) Un-allocated instruction codes are equivalent to BYPASS.7.2.1(c) There is no device ID register. 7.8.1(b) Single-step operationrequires external control of the system clock. 7.9.1(. . .) There as noRUNBIST facility. 7.11.1(. . .) There is no IDCODE instruction. 7.12.1(.. .) There is no USERCODE instruction. 8.1.1(b) There is no deviceidentification register. 8.2.1(c) Guaranteed for all publicinstructions. The apparent length of the path from tdi to tdo may changeunder certain circumstances while private instruction codes are loaded.9.3.1(d-i) Guaranteed for all public instructions. Data may be loaded attimes other than on the rising edge of tck while private instructionscodes are loaded. 10.4.1(e) During INTEST, the system clock pin must becontrolled externally. 10.6.1(c) During INTEST, output pins arecontrolled by data shifted in via tdi.

[1035] A. 8.2.2 Recommendations TABLE A.8.3 Recommendations metRecommendation Description 3.2.1(b) tck is a high-impedance CMOS input.3.3.1(c) tms has a high impedance pull-up. 3.6.1(d) (Applies to use ofchip). 3.7.1(a) (Applies to use of chip). 6.1.1(e) The SAMPLE/PRELOADinstruction code is loaded during Capture-IR. 7.2.1(f) The INTESTinstruction is supported. 7.7.1(g) Zeros are loaded at system outputpins during EXTEST. 7.7.2(h) All system outputs may be sethigh-impedance. 7.8.1(f) Zeros are loaded at system input pins duringINTEST. 8.1.1(d,e) Design-specific test data regtsters are not publiclyaccessible.

[1036] TABLE A.8.4 Recommendations not implemented RecommendationDescription 10.4.1(f) During EXTEST, the signal driven into the on-chiplogic from the system clock pin is that supplied externally.

[1037] A.8.2.3 Permissions TABLE A.8.5 Permissions met PermissionsDescription 3.2.1(c) Guaranteed for all public instructions. 6.1.1(f)The instruction register is not used to capture design-specificinformation. 7.2.1(g) Several additional public instructions areprovided. 7.3.1(a) Several private instruction codes are allocated.7.3.1(c) (Rule?) Such instructions codes are documented. 7.4.1(f)Additional codes perform identically to BYPASS. 10.1.1(i) Each outputpin has its own 3-state control. 10.3.1(h) A parallel latch is provided.10.3.1(i,j) During EXTEST, input pins are controlled by data shifted invia tdl. 10.6.1(d,e) 3-state cells are not forced inactive in theTest-Logic-Reset state.

[1038] Section A.9 Spatial Decoder

[1039] 30 MH, operation

[1040] Decodes MPEG, JPEG & H.261

[1041] Coded data rates to 25 Mb/s

[1042] Video data rates to 21 MB/s

[1043] Flexible chroma sampling formats

[1044] Full JPEG baseline decoding

[1045] Glue-less DRAM interface

[1046] Single −5V supply

[1047] 208 pin PQFP package

[1048] Max. power dissipation 2.5 W

[1049] Independent coded data and decoder clocks

[1050] Uses standard page mode DRAM

[1051] The Spatial Decoder is a configurable VLSI decoder chip for usein a variety of JPEG, MPEG and H.261 picture and video decodingapplications.

[1052] In a minimum configuration, with no off-chip DRAM, the SpatialDecoder is a single chip, high speed JPEG decoder. Adding DRAM allowsthe Spatial Decoder to decode JPEG encoded video pictures. 720×480, 30Hz, 4:2:2 ” JPEG video” can be decoded in real-time.

[1053] With the Temporal Decoder Temporal Decoder the Spatial Decodercan be used to decode H.261 and MPEG (as well as JPEG). 704×480, 30 Hz,4:2:0 MPEG video can be decoded.

[1054] Again, the above values are merely illustrative, by way ofexample and not necessarily by way of limitation, of typical values forone embodiment in accordance with the present invention. Accordingly,those of ordinary skill in the art will appreciate that other valuesand/or ranges may be used.

[1055] A.9.1 Spatial Decoder Signals TABLE A.9.1 Spatial Decoder signalsSignal Name I/O Pin Number Description coded_clock I 182 Coded Data PortUsed to supply coded_data[7:0] I 172, 171, 169, 168, coded data orTokens to the Spatal 167, 166, 164, 163 Decoder. coded_extn I 174 Seesections A.10.1 and A.4.1 coded_valid I 162 coded_accept O 161 byte_modeI 176 {overscore (enable)} [1:0] I 126, 127 Micro Processor Interface(MPI). r{overscore (w)} I 125 See section A.6.1 addr[6:0] I 136, 135,133, 132, 131, 130, 128 data[7:0] O 152, 151, 149, 147, 145, 143, 141,140 {overscore (irq)} O 154 DRAM_data[3:1:0] I/O 15, 17, 19, 20, 22, 25,27, 30, 31, DRAM Interface. 33, 35, 38, 39, 42, 44, 47, 49, 57, Seesection A.5.2 59, 61, 63, 66, 68, 70, 72, 74, 78 79, 81, 83, 84, 85DRAM_addr[10:0] O 184, 186, 188, 189, 192, 193, 195, 197, 199, 200, 203{overscore (RAS)} O 11 {overscore (CAS)} [3:0] O 2, 4, 6, 8 {overscore(WE)} O 12 {overscore (OE)} O 204 DRAM_enable I 112 out_data[8:0] O 88,89, 90, 92, 93, 94, 95, 97, 98 Output Port. out_extn O 87 See sectionA.4.1 out_valid O 99 out_accept I 100 tck I 115 JTAG port tci I 116 Seesection A.8 tco O 120 tms I 117 {overscore (trst)} I 121 decoder_clock I177 The main decoder clock, See section A.7 {overscore (reset)} I 160Reset.

[1056] TABLE A.9.2 Spatial Decoder Test signals Pin Signal Name I/O Num.Description tphDish I 122 If override = 1 then tph0ish and tph1ish aretph1ish I 123 inputs for the on-chip two phase clock. override I 110 Fornormal operation set override = 0. tph0ish and tph1ish are ignored (soconnect to GND or V_(DD)). chiptest I 111 Set chiptest = 0 for normaloperation. tloop I 114 Connect to GND or V_(DD) during normal operation.ramtest I 109 If ramtest = 1 test of the on-chip RAMs is enabled. Setramtest = 0 for normal operation. pilselect I 178 If pilselect = theon-chip phase locked loops are disabled. Set pilselect = 1 for normaloperation. ti I 180 Two clocks required by the DRAM interface tq I 179during test operation. Connect to GND or V_(DD) during normal operation.pdout O 207 These two pins are connections for an pdin I 206 externalfilter for the phase lock loop.

[1057] TABLE A.9.3 Spatial Decoder Pin Assignments Signal Name PinSignal Name Pin Signal Name Pin Signal Name Pin nc 208 nc 156 nc 104 nc52 test pin 207 nc 155 nc 103 nc 51 test pin 206 {overscore (irq)} 154nc 102 nc 50 GND 205 nc 153 VDD 101 DRAM_data[15] 49 OE 204 data[7] 152out_accept 100 nc 48 DRAM_addr[0] 203 data[6] 151 out_valid 99DRAM_data[16] 47 VDD 202 nc 150 out_data[0] 98 nc 46 nc 201 data[5] 149out_data[1] 97 GND 45 DRAM_addr[1] 200 nc 148 GND 96 DRAM_data[17] 44DRAM_addr[2] 199 data[4] 147 out_data[2] 95 nc 43 GND 198 GND 146out_data[3] 94 DRAM_data[18] 42 DRAM_addr[3] 197 data[3] 145 out_data[4]93 VDD 41 nc 196 nc 144 out_data[5] 92 nc 40 DRAM_addr[4] 195 data[2]143 VDD 91 DRAM_data [19] 39 VDD 194 nc 142 out_data[6] 90 DRAM_data[20]38 DRAM_addr[5] 193 data[1] 141 out_data[7] 89 nc 37 DRAM_addr[6] 192data[0] 140 out_data[8] 88 GND 36 nc 191 nc 139 out_extn 87DRAM_data[21] 35 GND 190 VDD 138 GND 86 nc 34 DRAM_addr[7] 189 nc 137DRAM_data[0] 85 DRAM_data[22] 33 DRAM_addr[8] 188 addr[6] 136DRAM_data[1] 84 VDD 32 VDD 187 addr[5] 135 DRAM_data[2] 83 DRAM_data[23]31 DRAM_addr[9] 186 GND 134 VDD 82 DRAM_data[24] 30 nc 185 addr[4] 133DRAM_data[3] 81 nc 29 DRAM_addr[10] 184 addr[3] 132 nc 80 GND 28 GND 183addr[2] 131 DRAM_data[4] 79 DRAM_data[25] 27 coded_clock 182 addr[1] 130GND 78 nc 26 VDD 181 VDD 129 nc 77 DRAM_data[26] 25 test pin 180 addr[0]128 DRAM_data[5] 76 nc 24 test pin 179 {overscore (enable)}[0] 127 nc 75VDD 23 test pin 178 {overscore (enable)}[1] 126 DRAM_data[6] 74DRAM_data[27] 22 decoder_clock 177 {overscore (rw)} 125 VDD 73 nc 21byte_mode 176 GND 124 DRAM_data[7] 72 DRAM_data[28] 20 GND 175 test pin123 nc 71 DRAM_data[29] 19 coded_extn 174 test pin 122 DRAM_data[8] 70GND 18 nc 208 nc 156 nc 104 nc 52 test pin 207 nc 155 nc 103 nc 51 testpin 206 {overscore (irq)} 154 nc 102 nc 50 GND 205 nc 153 VDD 101DRAM_data[15] 49 OE 204 data[7] 152 out_accept 100 nc 48 DRAM_addr[0]203 data[6] 151 out_valid 99 DRAM_data[16 ] 47 VDD 202 nc 150out_data[0] 98 nc 46 nc 201 data[5] 149 out_data[1] 97 GND 45DRAM_addr[1] 200 nc 148 GND 96 DRAM_data[17] 44 DRAM_addr[2] 199 data[4]147 out_data[2] 95 nc 43 GND 198 GND 146 out_data[3] 94 DRAM_data[18] 42DRAM_addr[3] 197 data[3] 145 out_data[4] 93 VDD 41 nc 196 nc 144out_data[5] 92 nc 40 DRAM_addr[4] 195 data[2] 143 VDD 91 DRAM_data [19]39 VDD 194 nc 142 out_data[6] 90 DRAM_data[20] 38 DRAM_addr[5] 193data[1] 141 out_data[7] 89 nc 37 DRAM_addr[6] 192 data[0] 140out_data[8] 88 GND 36 nc 191 nc 139 out_extn 87 DRAM_data[21] 35 GND 190VDD 138 GND 86 nc 34 DRAM_addr[7 ] 189 nc 137 DRAM_data[0] 85DRAM_data[22] 33 DRAM_addr[8] 188 addr[6] 136 DRAM_data[1] 84 VDD 32 VDD187 addr[5] 135 DRAM_data[2] 83 DRAM_data[23] 31 DRAM_addr[9] 186 GND134 VDD 82 DRAM_data[24] 30 nc 185 addr[4] 133 DRAM_data[3] 81 nc 29DRAM_addr[10] 184 addr[3] 132 nc 80 GND 28 GND 183 addr[2] 131DRAM_data[4] 79 DRAM_data[25] 27 coded_clock 182 addr[1] 130 GND 78 nc26 VDD 181 VDD 129 nc 77 DRAM_data[26] 25 test pin 180 addr[0] 128DRAM_data[5] 76 nc 24 test pin 179 {overscore (enable)}[0] 127 nc 75 VDD23 test pin 178 {overscore (enable)}[1] 126 DRAM_data[6] 74DRAM_data[27] 22 decoder_clock 177 {overscore (rw)} 125 VDD 73 nc 21byte_mode 176 GND 124 DRAM_data[7] 72 DRAM_data[28] 20 GND 175 test pin123 nc 71 DRAM_data[29] 19 coded_extn 174 test pin 122 DRAM_data[8] 70GND 18 nc 173 {overscore (trst)} 121 GND 69 DRAM_data[30] 17coded_data[7] 172 tdo 120 DRAM_data[9] 68 nc 16 coded_data[6] 171 nc 119nc 67 DRAM_data[31] 15 VDD 170 VDD 118 DRAM_data[10] 66 VDD 14coded_data[5] 169 trns 117 VDD 65 nc 13 coded_data[4] 168 tdi 116 nc 64{overscore (WE)} 12 coded_data[3] 167 tck 115 DRAM_data[11] 63{overscore (RAS)} 11 coded_data[2] 166 test pin 114 nc 62 nc 10 GND 165GND 113 DRAM_data[12] 61 GND 9 coded_data[1] 164 DRAM_enable 112 GND 60{overscore (CAS)}[0] 8 coded_data[0] 163 test pin 111 DRAM_data[13] 59nc 7 coded_valid 162 test pin 110 nc 58 {overscore (CAS)}[1] 6coded_accept 161 test pin 109 DRAM_data[14] 57 VDD 5 reset 160 nc 108VDD 56 {overscore (CAS)}[2] 4 VDD 159 nc 107 nc 55 nc 3 nc 158 nc 106 nc54 {overscore (CAS)}[3] 2 nc 157 nc 105 nc 53 nc 1

[1058] A.9.1.1 ” nc” No Connect Pins

[1059] The pins labeled nc in Table A.9.3 are not currently used thesepins should be left unconnected.

[1060] A.9.1.2 V_(DD) and GND Pins

[1061] As will be appreciated by one of ordinary skill in the art, allthe V_(DD) and GND pins provided should be connected to the appropriatepower supply. Correct device operation cannot be ensured unless all theV_(DD) and GND pins are correctly used.

[1062] A.9.1.3 Test Pin Connections for Normal Operation

[1063] Nine pins on the Spatial Decoder are reserved for internal testuse. TABLE A.9.4 Default test pin connections Pin number ConnectionConnect to GND for normal operation Connect to V_(DD) for normaloperation Leave Open Circuit for normal operation

[1064] A.9.1.4 JTAG Pins for Normal Operation See section A.8.1

[1065] A.9.2 Spatial Decoder Memory Map TABLE A.9.5 Overview of SpatialDecoder memory map Addr. (hex) Register Name See table 0x00 . . . 0x03Interrupt service area A.9.6 0x04 . . . 0x07 Input circuit registersA.9.7 0x08 . . . 0x0F Start code detector registers 0x10 . . . 0x15Buffer start-up control registers A.9.8 0x16 . . . 0x17 Not used 0x18 .. . 0x23 DRAM interface configuration registers A.9.9 0x24 . . . 0x26Buffer manager acess and keyhole registers A.9.10 0x27 Not used 0x28 . .. 0x2F Huffman decoder registers A.9.13 0x30 . . . 0x39 Inversequantiser registers A.9.14 0x3A . . . 0x3B Not used 0x3C Not used 0x3D .. . 0x3F Not used 0x40 . . . 0x7F Test registers

[1066] TABLE A.9.6 Interrupt services area registers Addr. (hex) Bitnum. Register Name Page references 0x00 7 chip_event CED_EVENT_0 6 notused 5 Illegal_length_count_event SCD_ILLEGAL_LENGTH_COUNT 4 reservedmay read 1 or 0 SCD_JPEG_OVERLAPPING_START 3 overlapping_start_eventSCD_NON_JPEG_OVERLAPPING_START 2 unrecognised_start_eventSCD_UNRECOGNISED_START 1 stop_after_picture_event SCD_STOP_AFTER_PICTURE0 non_aligned_start_event SCD_NON_ALIGNED_START 0x01 7 chip_maskCED_MASK_0 6 not used 5 Illegal_length_count_mask 4 reserved write 0 tothis location SCD_JPEG_OVERLAPPING_START 3non_jpeg_overlapping_start_mask 2 unrecognised_start_mask 1stop_after_picture_mask 0 non_aligned_start_mask 0x02 7idct_too_few_event IDCT_DEFF_NUM 6 idct_too_many_IDCT_SUPER_NUM 5accept_enable_event BS_STREAM_END_EVENT 4 target_met_eventBS_TARGET_MET_EVENT 3 counter_flushed_too_early_eventBS_FLUSH_BEFORE_TARGET_MET_EVENT 2 counter_flushed_event BS_FLUSH_EVENT1 parser_event DEMUX_EVENT 0 huffman_event HUFFMAN_EVENT 0x03 7Idct_too_few_mask 6 idct_too_many_mask 5 accept_enable_mask 4target_met_mask 3 counter_flushed_too_early_mask 2 counter_flushed_mask1 parser_mask 0 huffman_mask

[1067] TABLE A.9.7 Start code detector and input circuit registers Addr.(hex) Bit num. Register Name Page references 0x04 7 coded_busy 6enable_mpi_Input 5 coded_extn 4:0 not used 0x05 7:0 coded_data 0x04 7:0not used 0x07 7:0 not used 0x08 7:1 not used 0start_code_detector_access also input_circuit_access CED_SCD_ACCESS 0x097:4 not used CED_SCD_CONTROL 3 stop_after_picture 2discard_extension_data 1 discard_user_data 0 Ignore_non_aligned 0x0A 7:5not used CED_SCD_STATUS 4 insert_sequence_start 3 discard_all_data 2:0start_code_search 0x08 7:0 Test register length_count 0x0C 7:0 0x0D 7:2not used 1:0 start_code_detector_coding_standard 0x0E 7:0 start_value0x0F 7:4 not used 3:0 picture_number

[1068] TABLE A.9.8 Buffer start-up registers Page re- Addr. Bit feren-(hex) num. Register Name ces 0x10 7:1 not used 0 startup_accessCED_BS_ACCESS 0x11 7:3 not used 2:0 bit_count_prescale CED_BS_PRESCALE0x12 7:0 bit_count_target CED_BS_TARGET 0x13 7:0 bit_count CED_BS_COUNT0x14 7:1 not used 0 offchip_queue CED_BS_QUEUE 0x15 7:1 not used 0enable_stream CED_BS_ENABLE_NXT_STM

[1069] TABLE A.9.9 DRAM interface configuration registers Addr. Page(hex) Bit num. Register Name references 0x18 7:5 not used 4:0page_start_length CED_IT_PAGE_START_LENGTH 0x19 7:4 not used 3:0read_cycle_length 0x1A 7:4 not used 3:0 write_cycle_length 0:18 7:4 notused 3:0 refresh_cycle_length 0x1C 7:4 not used 3:0 CAS_falling 0x1D 7:4not used 3:0 RAS_falling 0x1E 7:1 not used 0 Interface_timing_access0x1F 7:0 refresh_Interval 0x20 7 not used 6:4 DRAM_addr_strength[2:0]3:1 CAS_strength[2:0] 0 RAS_stength[2] 0x21 7:6 RAS_strength[1:0] 5:3OEWE_strength[2:0] 2:0 DRAM_data_strength[2:0] 0x22 7 ACCESS bit for padstrength etc. ?not usedCED_DRAM_CONFIGURE 6 zero_buffers 5 DRAM_enable 4no_refresh 3:2 row_address_bits[1:0] 1:0 DRAM_data_width[1:0] 0x23 7:0Test registers CED_PLL_RES_CONFIG

[1070] TABLE A.9.10 Buffer manager access and keyhole registers PageAddr. (hex) Bit num. Register Name references 0x24 7:1 not used 0buffer_manager_access 0x25 7:6 not used 5:0buffer_manager_keyhole_address 0x26 7:0 buffer_manager_keyhole_data

[1071] TABLE A.9.11 Buffer manager extended address space Addr Bit (hex)num. Register Name Page references 0x00 7:0 not used 0x01 7:2 1:0cdb_base 0x02 7:0 0x03 7:0 0x04 7:0 not used 0x05 7:2 1:0 cdb_number0x06 7:0 0x07 7:0 0x08 7:0 not used 0x09 7:0 cdb_read 0x0A 7:0 0x0B 7:00x0C 7:0 not used 0x0D 7:0 cdb_number 0x0E 7:0 0x0F 7:0 0x10 7:0 notused 0x11 7:0 tb_base 0x12 7:0 0x13 7:0 0x14 7:0 not used 0x15 7:0tb_length 0x16 7:0 0x17 7:0 0x18 7:0 not used 0x19 7:0 tb_read 0x1A 7:00x1B 7:0 0x1C 7:0 not used 0x1D 7:0 tb_number 0x1E 7:0 0x1F 7:0 0x20 7:0not used 0x21 7:0 buffer_limit 0x22 7:0 0x23 7:0 0x24 7:4 not used 3cdb_full 2 cdb_empty 1 tb_full 0 tb_empty

[1072] TABLE A.9.12 Video demux registers Addr. Bit (hex) num. RegisterName Page references 0x28 7 demux_access CED_H_CTRL[7] 6:4huffman_error_code[2:0] CED_H_CTRL[6:4] 3:0 private huffman control bits[3] selects special CBP, [2] selects 4/8 bit fixed length CBP 0x29 7:0parser_error_code CED_H_DMUX_ERR 0x2A 7:4 not used 3:0demux_keyhole_address 0x2B 7:0 CED_H_KEYHOLE_ADDR 0x2C 7:0demux_keyhole_data CED_H_KEYHOLE 0x2D 7 dummy_last_pictureCED_H_ALU_REG0, r_dummy_last_frame_bit 6 field_info CED_H_ALU_REG0,r_field_info_bit 5:1 not used 0 continue CED_H_ALU_REG0, r_continue_bit0x2E 7:0 rom_revision CED_H_ALU_REG1 0x2F 7:0 private register 0x2F 7CED_H_TRACE_EVENT write 1 to single step. one will be read when the stephas been completed 6 CED_H_TRACE_MASK set to one to enter single stepmode 5 CED_H_TRACE_RST partial reset when sequenced 1,0 4:0 not used

[1073] TABLE A.9.13 Video demux extended address space Addr. Bit (hex)num. Register Name Page references 0x00 7:0 not used 0x0F 0x10 7:0horiz_pels r_horiz_pels 0x11 7:0 0x12 7:0 vert_pels r_vert_pels 0x13 7:00x14 7:2 not used 1:0 buffer_size r_buffer_size 0x15 7:0 0x16 7:4 notused 3:0 pel_aspect r_pel_aspect 0x17 7:2 not used 1:0 bit_rater_bit_rate 0x18 7:0 0x19 7:0 0x1A 7:4 not used 3:0 pic_rate r_pic_rate0x1B 7:1 not used 0 constrained r_constrained 0x1C 7:0 picture_type 0x1D7:0 h261_pic_type 0x1E 7:2 not used 1:0 broken_closed 0x1F 7:5 not used4:0 prediction_mode 0x20 7:0 vbv_delay 0x21 7:0 0x22 7:0 privateregister MPEG full_pel_fwd, JPEG pending_frame_change 0x23 7:0 privateregister MPEG full_pel_bwd, JPEG restart_index 0x24 7:0 private registerhoriz_mb_copy 0x25 7:0 plc_number 0x26 7:1 not used 1:0 max_h 0x27 7:1not used 1:0 max_v 0x28 7:0 private register scratch1 0x29 7:0 privateregister scratch2 0x2A 7:0 private register scratch3 0x2B 7:0 Nf MPEGunused1, H261 ingob 0x2C 7:0 private register MPEG first_group, JPEGfirst_scan 0x2D 7:0 private register MPEG in_picture 0x2E 7dummy_last_picture r_rom_control 6 field_info 5:1 not used 0 continue0x2F 7:0 rom_revision 0x30 7:2 not used 1:0 dc_huff_0 0x31 7:2 not used1:0 dc_huff_1 0x32 7:2 not used 1:0 dc_huff_2 0x33 7:2 not used 1:0dc_huff_3 0x34 7:2 not used 1:0 ac_huff_0 0x35 7:2 not used 1:0ac_huff_1 0x36 7:2 not used 1:0 ac_huff_2 0x37 7:2 not used 1:0ac_huff_3 0x38 7:2 not used 1:0 tq_0 r_tq_0 0x39 7:2 not used 1:0 tq_1r_tq_1 0x3A 7:2 not used 1:0 tq_2 r_tq_2 0x3B 7:2 not used 1:0 tq_3r_tq_3 0x3C 7:0 component_name_0 r_c_0 0x3D 7:0 component_name_1 r_c_10x3E 7:0 component_name_2 r_c_2 0x3F 7:0 component_name_3 r_c_3 0x40 7:0private registers 0x63 0x40 7:0 r_dc_pred_0 0x41 7:0 0x42 7:0r_dc_pred_1 0x43 7:0 0x44 7:0 r_dc_pred_2 0x45 7:0 0x46 7:0 r_dc_pred_30x47 7:0 0x48 7:0 not used 0x4F 0x50 7:0 r_prev_mhf 0x51 7:0 0x52 7:0r_prev_mvf 0x53 7:0 0x54 7:0 r_prev_mhb 0x55 7:0 0x56 7:0 r_prev_mvb0x57 7:0 0x58 7:0 not used 0x5F 0x60 7:0 r_horiz_mbent 0x61 7:0 0x62 7:0r_vert_mbent 0x63 7:0 0x64 7:0 horiz_macroblocks r_horiz_mbs 0x65 7:00x66 7:0 vert_macroblocks r_vert_mbs 0x67 7:0 0x68 7:0 private registerr_restart_cnt 0x69 7:0 0x6A 7:0 restart_interval r_restart_int 0x6B 7:00x6C 7:0 private register r_blk_h_cnt 0x6D 7:0 private registerr_blk_v_cnt 0x6E 7:0 private register r_compid 0x6F 7:0 max_component_idr_max_compid 0x70 7:0 coding_standard r_coding_std 0x71 7:0 privateregister r_pattern 0x72 7:0 private register r_twd_r_size 0x73 7:0private register r_bwd_r_size 0x74 7:0 not used 0x77 0x78 7:2 not used1:0 blocks_h_0 r_blk_h_0 0x79 7:2 not used 1:0 blocks_h_1 r_blk_h_1 0x7A7:2 not used 1:0 blocks_h_2 r_blk_h_2 0x7B 7:2 not used 1:0 blocks_h_3r_blk_h_3 0x7C 7:2 not used 1:0 blocks_v_0 r_blk_v_0 0x7D 7:2 not used1:0 blocks_v_1 r_blk_v_1 0x7E 7:2 not used 1:0 blocks_v_2 r_blk_v_2 0x7F7:2 not used 1:0 blocks_v_3 r_blk_v_3 0x7F 7:0 not used 0xFF 0x100 7:0dc_bits_0[15:0] CED_H_KEY_DC_CPB0 0x10F 0x110 7:0 dc_bits_1[15:0]CED_H_KEY_DC_CPB1 0x11F 0x120 7:0 not used 0x13F 0x140 7:0ac_bits_0[15:0] CED_H_KEY_AC_CPB0 0x14F 0x150 7:0 ac_bits_1[15:0]CED_H_KEY_AC_CPB1 0x15F 0x160 7:0 not used 0x17F 0x180 7:0 dc_zssss_0CED_H_KEY_ZSSSS_INDEX0 0x181 7:0 dc_zssss_1 CED_H_KEY_ZSSSS_INDEX1 0x1827:0 not used 0x187 0x188 7:0 ac_eob_0 CED_H_KEY_EOB_INDEX0 0x189 7:0ac_eob_1 CED_H_KEY_EOB_INDEX1 0x18A 7:0 not used 0x18B 0x18C 7:0ac_zrl_0 CED_H_KEY_ZRL_INDEX0 0x18D 7:0 ac_zrl_1 CED_H_KEY_ZRL_INDEX10x18E 7:0 not used 0x1FF 0x200 7:0 ac_huffval_0[161:0]CED_H_KEY_AC_ITOD_0 0x2AF 0x2B0 7:0 dc_huffval_0[11:0]CED_H_KEY_DC_ITOD_0 0x2BF 0x2C0 7:0 not used 0x2FF 0x300 7:0ac_huffval_1[161:0] CED_H_KEY_AC_ITOD_1 0x3AF 0x3B0 7:0dc_huffval_1[11:0] CED_H_KEY_DC_ITOD_1 0x3BF 0x3C0 7:0 not used 0x7FF0x800 7:0 private registers 0xACF 0x800 7:0 CED_KEY_TCOEFF_CPB 0x80F0x810 7:0 CED_KEY_CBP_CPB 0x81F 0x820 7:0 CED_KEY_MBA_CPB 0x82F 0x8307:0 CED_KEY_MVD_CPB 0x83F 0x840 7:0 CED_KEY_MTYPE_1_CPB 0x84F 0x850 7:0CED_KEY_MTYPE_P_CPB 0x85F 0x860 7:0 CED_KEY_MTYPE_B_CPB 0x86F 0x870 7:0CED_KEY_MTYPE_H.261_CPB 0x88F 0x880 7:0 not used 0x900 0x901 7:0CED_KEY_HDSTROM_0 0x902 7:0 CED_KEY_HDSTROM_1 0x903 7:0CED_KEY_HDSTROM_2 0x90F 0x910 7:0 not used 0xABF 0xAC0 7:0CED_KEY_DMX_WORD_0 0xAC1 7:0 CED_KEY_DMX_WORD_1 0xAC2 7:0CED_KEY_DMX_WORD_2 0xAC3 7:0 CED_KEY_DMX_WORD_3 0xAC4 7:0CED_KEY_DMX_WORD_4 0xAC5 7:0 CED_KEY_DMX_WORD_5 0xAC6 7:0CED_KEY_DMX_WORD_6 0xAC7 7:0 CED_KEY_DMX_WORD_7 0xAC8 7:0CED_KEY_DMX_WORD_8 0xAC9 7:0 CED_KEY_DMX_WORD_9 0xACA 7:0 not used 0xACB0xACC 7:0 CED_KEY_DMX_AINCR 0xACD 7:0 0xACE 7:0 CED_KEY_DMX_CC 0xACF 7:0

[1074] TABLE A.9.14 Inverse quantizer registers Addr. Bit (hex) num.Register Name Page references 7:1 not used 0x30 7:1 not used 0 iq_access0x31 7:2 not used 1:0 iq_coding_standard 0x32 7:5 not used 4:0 testregister iq_scale 0x33 7:2 not used 1:0 test register iq_component 0x347:2 not used 1:0 test register inverse_quantiser_(—) prediction_mode0x35 7:0 test register jpeg_indirection 0x36 7:2 not used 1:0 testregister mpeg_indirection 0x37 7:0 not used 0x38 7:0iq_table_keyhole_address 0x39 7:0 iq_table_keyhole_data

[1075] TABLE A.9.15 Iq table extended address space Addr. (hex) RegisterName Page references 0x00:0x3F JPEG inverse quantisation table 0 MPEGdefault intra table 0x40:0x7F JPEG inverse quantisation table 1 MPEGdefault non-intra table 0x80:0xBF JPEG inverse quantisation table 2 MPEGdown-loaded intra table 0xC0:0xFF JPEG inverse quantisation table 3 MPEGdown-loaded non-intra table

[1076] Section A.10 Coded Data Input

[1077] The system in accordance with the present invention, must knowwhat video standard is being input for processing. Thereafter, thesystem can accept either pre-existing Tokens or raw byte data which isthen placed into Tokens by the Start Code Detector.

[1078] Consequently, coded data and configuration Tokens can be suppliedto the Spatial Decoder via two routes:

[1079] The coded data input port

[1080] The microprocessor interface (MPI)

[1081] The choice over which route(s) to use will depend upon theapplication and system environment. For example, at low data rates itmight be possible to use a single microprocessor to both control thedecoder chip-set and to do the system bitstream de-multiplexing. In thiscase, it may be possible to do the coded data input via the MPI.Alternatively, a high coded data rate might require that coded data besupplied via the coded data port.

[1082] In some applications it may be appropriate to employee a mixtureof MPI and coded data port input.

[1083] A.10.The Coded Data Port TABLE A.10.1 Coded data port signalsInput/ Signal Name Output Description coded_clock Input A clockoperating at up to 30 MHz controlling the operation of the inputcircuit. coded_data[7:0] Input The standard 11 wires required toimplement a coded_extn Input Token Port transferring 8 bit data values.coded_valid Input See secton A.4 for an electrical descriptioncoded_accept Output of this interface. Circuits off-chip must packagethe coded data into Tokens. byte_mode Input When high this signalindicates that information is to be transferred across the coded dataport in byte mode rather than Token mode.

[1084] The coded data port in accordance with the present invention, canbe operated in two nodes: Token mode and byte mode.

[1085] A.10.1.1 Token Mode

[1086] In the present invention, if byte_mode is low, then the codeddata port operates as a Token Port in the normal way and accepts Tokensunder the control of coded_valid and coded_accept. See section A.4 fordetails of the electrical operation of this interface.

[1087] The signal byte_mode is sampled at the same time as data [7:0],coded_extn and coded_valid, i.e., on the rising edge of coded_clock.

[1088] A.10.1.2 Byte Mode

[1089] If, however, byte_mode is high, then a byte of data istransferred on data,7:01 under the control of the two wire interfacecontrol signals coded_valid and coded_accept. In this case, coded_extnis ignored. The bytes are subsequently assembled on-chip into DATATokens until the input mode is changed.

[1090] 1) First word (“Head”) of Token supplied in token mode.

[1091] 2) Last word of Token supplied (coded_extn goes low).

[1092] 3) First byte of data supplied in byte mode. A new DATA Token isautomatically created on-chip.

[1093] A.10.2 Supplying Data Via the MPI

[1094] Tokens can be supplied to the Spatial decoder via the MPI byaccessing the coded data input registers.

[1095] A.10.2.1 Writing Tokens Via the MPI

[1096] The coded data registers of the present invention are groupedinto two bytes in the memory map to allow for efficient data transfer.The 8 data bits, coded_data [7:0], are in one location and the controlregisters, coded_busy, enable_mpi_input and coded_extn are in a secondlocation. (See Table A.9.7)

[1097] When configured for Token input via the MPI, the current Token isextended with the current value of coded_extn each time a value iswritten into coded_data[7:0]. Software is responsible for settingcoded_extn to 0 before the last word of any Token is written tocoded_data[7:0].

[1098] For example, a DATA Token is started by writing 1 into coded_extnand then 0×04 into coded_data[7:0]. The start of this new DATA Tokenthen passes into the Spatial Decoder for processing.

[1099] Each time a new 8 bit value is written to coded_data[7:0;, thecurrent Token is extended. Coded_extn need only be accessed again whenterminating the current Token, e.g. to introduce another Token. The lastword of the current Token is indicated by writing 0 to coded_extnfollowed by writing the last word of the current Token into codeddata[7:0]. TABLE A.10.2 Coded data input registers Register nameSize/Dir. Reset State Description coded_extn 1 x Tokens can be suppliedto the Spatial Decoder rw via the MPI by writing to these registers.coded_data [7:0] 8 x w coded_busy 1 1 The state of this registersindicates if the Spatial r Decoder is able to accept Tokens written intocoded_data [7:0]. The value 1 indicates that the interface is busy andunable to accept data. Behaviour is undefined if the user tries to writeto coded_data[7:0] when coded_busy = 1. enable_mpi-input 1 0 The valuein this function enable registers rw controls whether coded data inputto the Spatial Decoder is via the coded data port (0) or via the MPI(1).

[1100] Each time before writing to coded_data[7:0], coded_busy should beinspected to see if the interface is ready to accept more data.

[1101] A.10.3 Switching Between Input Modes

[1102] Provided suitable precautions are observed, it is possible todynamically change the data input mode. In general, the transfer of aToken via any one route should be completed before switching modes.TABLE A.10.3 Switching data input modes Previous Mode Next ModeBehaviour Byte Token The on-chip circuitry will use the last bytesupplied in MPI input byte mode as the last byte of the DATA Token thatit was constructing (i.e. the extn bit will be set to 0). Beforeaccepting the next token. Token Byte The off-chip circuitry supplyingthe Token in Token mode is responsible for completing the Token (i.e.with the extn bit of the last byte of information set to 0) beforeselecting byte mode. MPI input Access to input via the MPI will not begranted (i.e. coded_busy will remain set to 1) until the off-chipcircuitry supplying the Token in Token mode has completed the Token(i.e. with the extn bit of the last byte of information set to 0). MPIinput Byte The control software must have completed the Token MPI input(i.e. with the extn bit of the last byte of information set to 0) beforeenable_mpi_input is set to 0.

[1103] The first byte supplied in byte mode causes a DATA Token headerto be generated on-chip. Any further bytes transferred in byte mode arethereafter appended to this DATA Token until the input mode changes.Recall, DATA Tokens can contain as many bits as are necessary.

[1104] The MPI register bit, coded busy, and the signal, coded_accept,indicate on which interface the Spatial decoder is willing to acceptdata. Correct observation of these signals ensures that no data is lost.

[1105] A.10.4 Rate of Accepting Coded Data

[1106] In the present invention, the input circuit passes Tokens to theStart Code Detector (see section A.11). The Start code Detector analysesdata in the DATA Tokens bit serially. The Detector's normal rate ofprocessing is one bit per clock cycle (of coded_clock). Accordingly, itwill typically decode a byte of coded data every 8 cycles ofcoded_clock. However, extra processing cycles are occasionally required,e.g., when a non-DATA Token is supplied or when a start code isencountered in the coded data. When such an event occurs, the Start CodeDetector will, for a short time, be unable to accept more information.

[1107] After the Start Code Detector, data passes into a first logicalcoded data buffer. If this buffer fills, then the Start Code Detectorwill be unable to accept more information.

[1108] Consequently, no more coded data (or other Tokens) will beaccepted on either the coded data port, or via the MPI, while the StartCode Detector is unable to accept more information. This will beindicated by the state of the signal coded_accept and the registercoded_busy.

[1109] By using coded_accept and/or coded_busy, the user is guaranteedthat no coded information will be lost. However, as will be appreciatedby one of ordinary skill in the art, the system must either be able tobuffer newly arriving coded data (or stop new data for arriving) if theSpatial decoder is unable to accept data.

[1110] A.10.5 Coded Data Clock

[1111] In accordance with the present invention, the coded data port,the input circuit and other functions in the Spatial Decoder arecontrolled by coded_clock. Furthermore, this clock can be asynchronousto the main decoder_clock. Data transfer is synchronized todecoder_clock on-chip.

[1112] SECTION A.11 Start Code Detector

[1113] A.11.1 Start Codes

[1114] As is well known in the art, MPEG and H.261 coded video streamscontain identifiable bit patterns called start codes. A similar functionis served in JPEG by marker codes. Start/marker codes identifysignificant parts of the syntax of the coded data stream. The analysisof start/marker codes performed by the Start Code Detector is the firststage in parsing the coded data. The Start Code Detector is the firstblock on the Spatial Decoder following the input circuit.

[1115] The start/marker code patterns are designed so that they can beidentified without decoding the entire bitstream. Thus, they can be usedin accordance with the present invention, to help with error recoveryand decoder start-up. The Start Code Detector provides facilities todetect errors in the coded data construction and to assist the start-upof the decoder.

[1116] A.11.2 Start Code Detector Registers

[1117] As previously discussed, many of the Start Code Detectorregisters are in constant use by the Start Code Detector. So, accessingthese registers will be unreliable if the Start Code Detector isprocessing data. The user is responsible for ensuring that the StartCode Detector is halted before accessing its registers.

[1118] The register start_code_detector access is used to halt the StartCode Detector and so allow access to its registers. The Start CodeDetector will halt after it generates an interrupt.

[1119] There are further constraints on when the start code search anddiscard all data modes can be initiated. These are described in A.11.8and A.11.5.1. TABLE A.11.1 Start code detector test registers Registername Size/Dir. Reset State Description start_code_detector_access 1 0Writing 1 to this register requests that the start rw code detector stopto allow access to its registers. The user should wait until the value 1can be read from this register indicating that operation has stopped andaccess is possible. illegal_length_count_event 1 0 An illegal lengthcount event will occur if rw while decoding JPEG data, a length countfield is found carrying a value less than 2. This should only occur asthe result of an error in the JPEG data. illegal_length_count_mask 1 0If the mask register is set to 1 then an rw interrupt can be generatedand the start code detector will stop. Behaviour following an error isnot predictable if this error is suppressed (mask register set to 0).See A.11.4.1. jpeg_overlapping_start_event 1 0 If the coding standard isJPEG and the rw sequence 0xFF 0xFF is found whilejpeg_overlapping_start_mask 1 0 looking for a marker code this eventwill rw occur. This sequence is a legal stuffing sequence. If the maskregister is set to 1 then an interrupt can be generated and the startcode detector will stop. See A.11.4.2. overlapping_start_event 1 0 Ifthe coding standard is MPEG or H.261 rw and an overlapping start code isfound overlapping_start_mask 1 0 while looking for a start code thiseven will rw occur. If the mask register is set to 1 then an interruptcan be generated and the start code detector will stop. See A.11.4.2.unrecognised_start_event 1 0 If an unrecognised start code is rwencountered this event will occur. If the mask register is set to 1 thenan interrupt unrecognised_start_mask 1 0 can be generated and the startcode rw detector will stop. start_value 8 x The start code value readfrom the ro bitstream is available in the register start_value while thestart code detector is halted. See A.11.4.3 During normal operationstart_value contains the value of the most recently decoded start/markercode. Only the 4 LSBs of start_value are used during H.261 operation.The 4 MSBs will be zero. stop_after_picture_event 1 0 If the registerstop_after_picture is set to rw 1 then a stop after picture event willbe stop_after_picture_mask 1 0 generated after the end of a picture hasrw passed through the start code detector. stop_after_picture 1 0 If themask register is set to 1 then an rw interrupt can be generated and thestart code detector will stop. See A.11.5.1 stop_after_picture does notreset to 0 after the end of a picture has been detected so should becleared directly. non_aligned_start_event 1 0 When ignore_non_aligned isset to 1, start rw codes that are not byte aligned are ignored (treatedas normal data) non_aligned_start_mask 1 0 When ignore_non_aligned isset to 0, H.261 rw and MPEG start codes will be detected regardless ofbyte alignment and the non- aligned start event will be generated. Ifthe mask register is set to 1 then the event will cause an interrupt andthe start code detector will stop. See A.11.6. ignore_non_aligned 1 0 Ifthe coding standard is configured as rw JPEG Ignore_non_aligned isignored and the non-aligned start event will never be generated.discard_extension_data 1 0 When these registers are set to 1 extensionrw or user data that cannot be decoded by the discard_user_data 1 0Spatial Decoder is discarded by the start rw code detector. SeeA.11.3.3. discard_all_data 1 0 When set to 1 all data and Tokens are rwdiscarded by the start code detector. This continues until a FLUSH Tokenis supplied or the register is set to 0 directly. The FLUSH Token thatresets this register is discarded and not output by the start codedetector. See A.11.5.1. insert_sequence_start 1 See A.11.7 rwstart_code_search 3 5 When this register is set to 0 the start rw codedetector operates normally. When set to a higher value the start codedetector discards data until the specified type of start code isdetected. When the specified start code is detected the register is setto 0 and normal operation follows. See A.11.8.start_code_detector_coding_standard 2 0 This register configures thecoding rw standard used by the start code detector. The register can beloaded directly or by using a CODING_STANDARD Token. Whenever the startcode detector generates a CODING_STANDARD Token (see A.11.7.4) itcarries its current coding standard configuration. This Token will thenconfigure the coding standard used by all other parts of the decoderchip-set. See A.21.1 on page 180 and A.11.7. picture_number 4 0 Eachtime the start coded detector rw detects a picture start code in thedata stream (or the H.261 or JPEG equivalent) a PICTURE_START Token isgenerated which carries the current value of picture_number. Thisregister then increments.

[1120] TABLE A.11.2 Start code detector test registers Register nameSize/Dir. Reset State Description length_count 16 0 This registercontains the r0 current value of the JPEG length count. This register ismodified under the control of the coded data clock and should only beread via the MPI when the start code detector is stopped.

[1121] A.11.3 Conversion of Start Codes to Tokens

[1122] In normal operation the function of the Start Code Detector is toidentify start codes in the data stream and to then convert them to theappropriate start code Token. In the simplest case, data is supplied tothe Start code Detector in a single long DATA Token. The output of theStart Code Detector is a number of shorter DATA Tokens interleaved withstart code Tokens.

[1123] Alternatively, in accordance with the present invention, theinput data to the Start Code Detector could be divided up into a numberof shorter DATA Tokens. There is no restriction on how the coded data isdivided into DATA Tokens other than that each DATA Token must contain8×n bits where n is an integer.

[1124] Other Tokens can be supplied directly to the input of the StartCode Detector. In this case, the Tokens are passed through the StartCode Detector with no processing to other stages of the spatial Decoder.These Tokens can only be inserted just before the location of a startcode in the coded data.

[1125] A.11.3.1 Start Code Formats

[1126] Three different start code formats are recognized by the StartCode Detector of the present invention. This is configured via theregister, start_code_detector_coding_standard. TABLE A.11.3 Start codeformats Coding Standard Start Code Pattern (hex) Size of start codevalue MPEG 0x00 0x00 0x01 <value> 8 bit JPEG 0xFF <value> 8 bit H.2610x00 0x01 <value> 4 bit

[1127] A.11.3.2 Start Code Token Equivalents

[1128] Having detected a start code, the Start Code Detector studies thevalue associated with the start code and generates an appropriate Token.In general, the Tokens are named after the relevant MPEG syntax.However, one of ordinary skill in the art will appreciate that theTokens can follow additional naming formats. The coding standardcurrently selected configures the relationship between start code valueand the Token generated. This relationship is shown in Table A.11.4.TABLE A.11.4 Tokens from start code values Start Code Value MPEG H.251JPEG JPEG Start code Token generated (hex) (hex) (hex) (name)PICTURE_START 0x00 0x00 0xDA SOS SLICE_START^(a) 0x01 to 0x01 to 0xD0 toRST₀ to 0xAF 0x0C 0xD7 RST_($$) SEQUENCE_START 0xB3 0xD8 SOISEOUENCE_END 0xB7 0xD9 ECI GROUP_START 0xB8 0XC0 SCF₀ ^(b) USER_DATA0xB2 0xE0 to APP₀ to 0xEF APP_($$) 0xFE COM EXTENSION_DATA 0xB5 0xC8 JPG0xF0 to JPG₀ to 0xFD JPG₀ 0x02 to RES 0xBF 0xC1 to SOF₁ to 0xCB SOF₁₁0xCC DAC DHT_MARKER 0xC4 DHT DNL_MARKER 0xDC DNL DQT_MARKER 0xDB DQTDRI_MARKER 0xDD DRI

[1129] A.11.3.3 Extended Features of the Coding Standards

[1130] The coding standards provide a number of mechanisms to allow datato be embedded in the data stream whose use is not currently defined bythe coding standard. This might be application specific “user data” thatprovides extra facilities for a particular manufacturer. Alternatively,it might be “extension data”. The coding standards authorities reservedthe right to use the extension data to add features to the codingstandard in the future.

[1131] Two distinct mechanisms are employed. JPEG precedes blocks ofuser and extension data with marker codes. However, H.261 inserts “extrainformation” indicated by an extra information bit in the coded data.MPEG can use both these techniques.

[1132] In accordance with the present invention, MPEG/JPEG blocks ofuser and extension data preceded by start/marker codes can be detectedby the Start Code Detector. H.261/MPEG “extra information” is detectedby the Huffman decoder of the present invention. See A.14.7, ” ReceivingExtra Information”.

[1133] The registers, discard_extension_data and discard_user_data,allow the Start Code Detector to be configured to discard user data andextension data. If this data is not discarded at the Start Code Detectorit can be accessed when it reaches the Video Demux see A.14.6,“Receiving User and Extension data”.

[1134] The Spatial Decoder of the present invention supports thebaseline features of JPEG. The non-baseline features of JPEG are viewedas extension data by the Spatial Decoder. So, all JPEG marker codes thatprecede data for non-baseline JPEG are treated as extension data.

[1135] A.21.3.4 JPEG Table Definitions

[1136] JPEG supports down loaded Huffman and quantizer tables. In JPEGdata, the definition of these tables is preceded by the marker codes DNLand DQT. The Start Code Detector generates the Tokens DHT_MARKER andDQT_MARKER when these marker codes are detected. These Tokens indicateto the Video Demux that the DATA Token which follows contains coded datadescribing Huffman or quantizer table (using the formats described inJPEG).

[1137] A.11.4 Error Detection

[1138] The Start Code Detector can detect certain errors in the codeddata and provides some facilities to allow the decoder to recover afteran error is detected (see A.11.9, “Start code searching”).

[1139] A.11.4.1 Illegal JPEG Length Count

[1140] Most JPEG marker codes have a 16 bit length count fieldassociated with them. This field indicates how much data is associatedwith this marker code. Length counts of 0 and I are illegal. An illegallength should only occur following a data error. In the presentinvention, this will generate an interrupt if illegal_length_count_maskis set to 1.

[1141] Recovery from errors in JPEG data is likely to require additionalapplication specific data due to the difficulty of searching for startcodes in JPEG data (see A.11.8.1).

[1142] A.11.4.2 Overlapping Start/Marker Codes

[1143] In the present invention, overlapping start codes should onlyoccur following a data error. An MPEG, byte aligned, overlapping startcode is illustrated in FIG. 64. Here, the Start Code Detector-first seesa pattern that looks like a picture start code. Next the Start CodeDetector sees that this picture start code is overlapped with a groupstart. Accordingly, the Start Code Detector generates a overlappingstart event. Furthermore, the Start Code Detector will generate aninterrupt and stop if overlapping_start_mask is set to 1.

[1144] It is impossible to tell which of the two start codes is thecorrect one and which was caused by a data error. However, the StartCode Detector in accordance with the present invention, discards thefirst start code and will proceed decoding the second start code “as ifit is correct” after the overlapping start-code event has been serviced.If there are a series of overlapped start codes, the Start Code Detectorwill discard all but the last (generating an event for each overlappingstart code).

[1145] Similar errors are possible in non byte-aligned systems (H.261 orpossibly MPEG). In this case, the state of ignore_non_aligned must alsobe considered. FIG. 65 illustrates an example where the first start codefound is byte aligned, but it overlaps a non-aligned start code. Ifignore_non_aligned is set to 1, then the second overlapping start codewill be treated as data by the Start Code Detector and, therefore nooverlapping start code event will occur. This conceals a possible datacommunications error. If ignore_non_aligned is set to 0, however theStart Code Detector will see the second, non aligned, start code andwill see that it overlaps the first start code.

[1146] A.11.4.3 Unrecognized Start Codes

[1147] The Start Code Detector can generate an interrupt when anunrecognized start code is detected (if unrecognized_start_mask =1). Thevalue of the start code that caused this interrupt can be read from theregister start_value.

[1148] The start code value 0xB4 (sequence error) is used in MPEGdecoder systems to indicate a channel or media error. For example, thisstart code may be inserted into the data by an ECC circuit if it detectsan error that it was unable to correct.

[1149] A.11.4.4 Sequence of Event Generation

[1150] In the present invention, certain coded data patterns (probablyindicating an error condition) will cause more than one of the aboveerror conditions to occur within a short space of time. Consequently,the sequence in which the Start Code Detector examines the coded datafor error conditions is:

[1151] 1) Non-aligned start codes

[1152] 2) Overlapping start codes

[1153] 3) Unrecognized start codes

[1154] Thus, if a non-aligned start code overlaps another, later, startcode, the first event generated will be associated with the non-alignedstart code. After this event has been serviced, the Start CodeDetector's operation will proceed, detecting the overlapped start code ashort time later.

[1155] The Start Code Detector only attempts to recognize the start codeafter all tests for non-aligned and overlapping start codes arecomplete.

[1156] A.11.5 Decoder Start-up and Shutdown

[1157] The Start Code Detector provides facilities to allow the currentdecoding task to be completed cleanly and for a new task to be started.

[1158] There are limitations on using these techniques with JPEG codedvideo as data segments can contain values that emulate marker codes (seeA.11.8.1).

[1159] A.11.5.1 Clean End to Decoding

[1160] The Start Code Detector can be configured to generate aninterrupt and stop once the data for the current picture is complete.This is done by setting stop_after_picture=1 andstop_after_picture_mask=1.

[1161] Once the end of a picture passes through the Start Code Detector,a FLUSH Token is generated (A.11.7.2), an interrupt is generated, andthe Start Code Detector stops. Note that the picture just completed willbe decoded in the normal way. In some applications, however, it may beappropriate to detect the FLUSH arriving at the output of the decoderchip-set as this will indicate the end of the current video sequence.For example, the display could freeze on the last picture output.

[1162] When the Start Code Detector stops, there may be data from the“old” video sequence “trapped” in user implemented buffers between themedia and the decode chips. Setting the register, discard_all_data, willcause the Spatial Decoder to consume and discard this data. This willcontinue until a FLUSH Token reaches the Start Code Detector ordiscard_all_data is reset via the microprocessor interface.

[1163] Having discarded any data from the “old” sequence the decoder isnow ready to start work on a new sequence.

[1164] A.11.5.2 When to Start Discard all Mode

[1165] The discard all mode will start immediately after a 1 is writteninto the discard_all_data register. The result will be unpredictable ifthis is done when the Start Code Detector is actively processing data.

[1166] Discard all mode can be safely initiated after any of the StartCode Detector events (non-aligned start event etc.) has generated aninterrupt.

[1167] A.11.5.3 Starting a New Sequence

[1168] If it is not known where the start of a new coded video sequenceis within some coded data, then the start code search mechanism can beused. This discards any unwanted data that precedes the-start of thesequence. See A.11.a.

[1169] A.11.5.4 Jumping Between Sequences

[1170] This section illustrates an application of some of the techniquesdescribed above. The objective is to “jump” from one part of one codedvideo sequence to another. In this example, the filing system onlyallows access to “blocks” of data. This block structure might be derivedfrom the sector size of a disc or a block error correction system. So,the position of entry and exit points in the coded video data may not berelated to the filing system block structure.

[1171] The stop_after_picture and discard_all_data mechanisms allowunwanted data from the old video sequence to be discarded. Inserting aFLUSH Token after the end of the last filing system data block resetsthe discard_all_data mode. The start code search mode can then be usedto discard any data in the next data block that precedes a suitableentry point.

[1172] A.11.6 Byte Alignment

[1173] As is well known in the art, the different coding schemes havequite different views about byte alignment of start/marker codes in thedata stream.

[1174] For example, H.261 views communications as being bit serial.Thus, there is no concept of byte alignment of start codes. By settingignore_non_aligned=0 the Start Code Detector is able to detect startcodes with any bit alignment. By setting non-aligned_start_mask=0, thestart code non-alignment interrupt is suppressed. In contrast, however,JPEG was designed for a computer environment where byte alignment isguaranteed. Therefore, marker codes should only be detected when bytealigned. When the coding standard is configured as JPEG, the registerignore_non_aligned is ignored and the non-aligned start event will neverbe generated. However, setting ignore_non_aligned=1 andnon_aligned_start_mask=0 is recommended to ensure compatibility withfuture products.

[1175] MPEG, on the other hand, was designed to meet the needs of bothcommunications (bit serial) and computer (byte oriented) systems. Startcodes in MPEG data should normally be byte aligned. However, thestandard is designed to be allow bit serial searching for start codes(no MPEG bit pattern, with any bit alignment, will look like a startcode, unless it is a start code). So, an MPEG decoder can be designedthat will tolerate loss of byte alignment in serial data communications.

[1176] If a non-aligned start code is found, it will normally indicatethat a communication error has previously occurred. If the error is a“bit-slip” in a bit-serial communications system, then data containingthis error will have already been passed to the decoder. This error islikely to cause other errors within the decoder. However, new dataarriving at the Start Code Detector can continue to be decoded afterthis loss of byte alignment.

[1177] By setting ignore_non_aligned=0 and non_aligned_start_mask=1, aninterrupt can be generated if a non-aligned start code is detected. Theresponse will depend upon the application. All subsequent start codeswill be non-aligned (until byte alignment is restored). Accordingly,setting non_aligned_start_mask=0 after byte alignment has been lost maybe appropriate. TABLE A.11.5 Configuring for byte alignment MPEG JPEGH.251 ignore_non_aligned 0 1 0 non_aligned_start_mask 1 0 0

[1178] A.11.7 Automatic Token Generation

[1179] In the present invention, most of the Tokens output by the StartCode Detector directly reflect syntactic elements of the various pictureand video coding standards. In addition to these “natural” Tokens, someuseful “invented” Tokens are generated. Examples of these proprietarytokens are PICTURE_END and CODING_STANDARD. Tokens are also introducedto remove some of the syntactic differences between the coding standardsand to 'tidy up” under error conditions.

[1180] This automatic Token generation is done after the serial analysisof the coded data (see FIG. 61, “The Start Code Detector”). Thereforethe system responds equally to Tokens that have been supplied directlyto the input of the Spatial Decoder via the Start Code Detector and toTokens that have been generated by the Start Code Detector following thedetection of start codes in the coded data.

[1181] A.11.7.1 Indicating the End of a Picture

[1182] In general, the coding standards don't explicitly signal the endof a picture. However, the Start Code Detector of the present inventiongenerates a PICTURE_END Token when it detects information that indicatesthat the current picture has been completed.

[1183] The Tokens that cause PICTURE_END to be generated are:SEQUENCE_START, GROUP_START, PICTURE_START, SEQUENCE_END and FLUSH.

[1184] A.11.7.2 Stop After Picture End Option

[1185] If the register stop_after_picture is set, then the Start CodeDetector will stop after a PICTURE_END Token has passed through.However, a FLUSH Token is inserted after the PICTURE_END to “push” thetail end of the coded data through the decoder and to reset the system.See A.11.5.1.

[1186] A.11.7.3 Introducing Sequence Start for H.261

[1187] H.261 does not have a syntactic element equivalent to sequencestart (see Table A.11.4). If the register insert_sequence_start is set,then the Start Code Detector will ensure that there is oneSEQUENCE_START Token before the next PICTURE_START, i.e., if the StartCode Detector does not see a SEQUENCE_START before a PICTURE_START, onewill be introduced. No SEQUENCE_START will be introduced if one isalready present.

[1188] This function should not be used with NPEG or JPEG.

[1189] A.11.7.4 Setting Coding Standard for Each Sequence

[1190] All SEQUENCE_START Tokens leaving the Start Code Detector arealways preceded by a CODING_STANDARD Token. This Token is loaded withthe Start Code Detector's current coding standard. This sets the codingstandard for the entire decoder chip set for each new video sequence.

[1191] A.11.8 Start Code Searching

[1192] The Start Code Detector in accordance with the invention, can beused to search through a coded data stream for a specified type of startcode. This allows the decoder to re-commence decoding from a specifiedlevel within the syntax of some coded data (after discarding any datathat precedes it). Applications for this include:

[1193] start-up of a decoder after jumping into a coded data file at anunknown position (e.g., random accessing).

[1194] to seek to a known point in the data to assist recovery after adata error.

[1195] For example, Table A.11.6 shows the MPEG start codes searched,for different configurations of start_code_search. The equivalent H.261and JPEG start/marker codes can be seen in Table A.11.4. TABLE A.11.6Start code search modes start_code_search Start codes searched for ...0^(a) Normal coeration 1 Reserved (will behave as discard data) 2 3sequence start 4 group or sequence start 5^(b) picture, group orsequence start 6 slice, picture, group or sequence start 7 the nextstart or marker code

[1196] When a non-zero value is written into the start_code_searchregister, the Start Code Detector will start to discard all incomingdata until the specified start code is detected. The start_code_searchregister will then reset to 0 and normal operation will continue.

[1197] The start code search will start immediately after a non-zerovalue is written into the start_code_search register. The result will beunpredictable if this is done when the Start Code Detector is activelyprocessing data. So, before initiating a start code search, the StartCode Detector should be stopped so no data is being processed. The StartCode Detector is always in this condition if any of the Start CodeDetector events (non-aligned start event etc.) has just generated aninterrupt.

[1198] A.118.1 Limitations on Using Start Code Search with JPEG

[1199] Most JPEG marker codes have a.16 bit length count fieldassociated with them. This field indicates the length of a data segmentassociated with the marker code. This segment may contain values thatemulate marker codes. In normal operation, the Start Code Detectordoesn't look for start codes in these segments of data.

[1200] If a random access into some JPEG coded data “lands” in such asegment, the start code search mechanism cannot be used reliably. Ingeneral, JPEG coded video will require additional external informationto identify entry points for random access.

[1201] SECTION A.12 Decoder Start-up Control

[1202] A.12.1 Overview of Decoder Start-up

[1203] In a decoder, video display will normally be delayed a short timeafter coded data is first available. During this delay, coded dataaccumulates in the buffers in the decoder. This pre-filling of thebuffers ensures that the buffers never empty during decoding and, this,therefore ensures that the decoder is able to decode new pictures atregular intervals.

[1204] Generally, two facilities are required to correctly start-up adecoder. First, there must be a mechanism to measure how much data hasbeen provided to the decoder.

[1205] Second, there must be a mechanism to prevent the display of a newvideo stream. The Spatial Decoder of the invention provides a bitcounter near its input to measure how much data has arrived and anoutput gate near its output to prevent the start of new video streambeing output.

[1206] There are three levels of complexity for the control of thesefacilities:

[1207] output gate always open

[1208] Basic control

[1209] Advanced control

[1210] With the output gate always open, picture output will start assoon as possible after coded data starts to arrive at the decoder. Thisis appropriate for still picture decoding or where display is beingdelayed by some other mechanism.

[1211] The difference between basic and advanced control relates to howmany short video streams can be accommodated in the decoder's buffers atany time. Basic control is sufficient for most applications. However,advanced control allows user software to help the decoder manage thestart-up of several very short video streams.

[1212] A.12.2 MPEG Video Buffer Verifier

[1213] MPEG describes a “video buffer verifier” (VBV) for constant datarate systems. Using the VBV information allows the decoder to pre-fillits buffers before it starts to display pictures. Again, thispre-filling ensures that the decoder's buffers never empty duringdecoding.

[1214] In summary, each MPEG picture carries a vbv_delay parameter. Thisparameter specifies how long the coded data buffer of an “ideal decoder”should fill with coded data before the first picture is decoded. Havingobserved the start-up delay for the first picture, the requirements ofall subsequent pictures will be met automatically.

[1215] MPEG, therefore, specifies the start-up requirements as a delay.However, in a constant bit rate system this delay can readily beconverted to a bit count. This is the basis on which the start-upcontrol of the Spatial Decoder of the present invention operates.

[1216] A.12.3 Definition of a Stream

[1217] In this application, the term stream is used to avoid confusionwith the MPEG term sequence. Stream therefore means a quantity of videodata that is “interesting” to an application. Hence, a stream could bemany MPEG sequences or it could be a single picture.

[1218] The decoder start-up facilities described in this chapter relateto meeting the VBV requirements of the first picture in a stream. Therequirements of subsequent pictures in that stream are metautomatically.

[1219] A.12.4 Start-up Control Registers TABLE A.12.1 Decoder start-upregisters Register name Size/Dif. Reset State Description startup_access1 0 Writing 1 to this register requests that the bit CED_BS_ACCESS rwcounter and gate opening logic stop to allow access to theirconfiguration registers. bit_count 8 0 This bit counter is incrementedas added data CED_BS_COUNT rw leaves the start code detector. The numberof bit_count_prescale 3 0 bits required to increment bit_count $$CED_BS_PRESCALE rw approx. 2^((bit) _(—count)_prescale$$ x 512. The bitcounter starts counting bits after a FLUSH Token passes through the bitcounter. It is reset to zero and then stops incrementing after the bitcount target has been met. bit_count_target 8 x This register specifiesthe bit count targer. A CED_BS_TARGET rw target met event is generatedwherever the following condition becomes true: bit_count >=bit_count_target target_met_event 1 0 When the bit count target is metthis event will BS_TARGET_MET_EVENT rw be generated. If the maskregister is set to 1 target_met_mask 1 0 then an interrupt can begenerated however. rw the bit counter will NOT stop processing data.This event will occur when the bit counter increments to its target. Itwill also count of a target value is written which is less than or equalto the current value of the bit counter Writing 0 to bit_count_targetwill always generate a target met event. accept_enable_event 1 0 Thisevent indicates that a FLUSH Token has BS_STREAM_END_EVENT rw passedthrough the output gate (causing it to accept_enable_mask 1 0 close) andthat an enable was available to allow rw the gate to open. If the maskregister is set to 1 then an interrupt can be generated and the registerenable_stream will be reset. See A.12.7.1

[1220] A.12.5 Output Gate Always Open

[1221] The output gate can be configured to remain open. Thisconfiguration is appropriate where still pictures are being decoded, orwhen some other mechanism is available to manage the start-up of thevideo decoder.

[1222] The following configurations are required after reset (havinggained access to the start-up control logic by writing 1 tostartup_access):

[1223] set offchip_queue=1

[1224] set enable_stream=1

[1225] ensure that all the decoder start-up event mask registers are setto 0 disabling their interrupts (this is the default state after reset).

[1226] (See A.12.7.1 for an explanation of why this holds the outputgate open.)

[1227] A.12.6 Basic Operation

[1228] In the present invention, basic control of the start-up logic issufficient for the majority of MPEG video applications. In this mode,the bit counter communicates directly with the output gate. The outputgate will close automatically as the end of a video stream passesthrough it as indicated by a FLUSH Token. The gate will remain closeduntil an enable is provided by the bit counter circuitry when a streamhas attained its start-up bit count.

[1229] The following configurations are required after reset (havinggained access to the start-up control logic by writing 1 tostartup_access):

[1230] set bit_count_prescale approximately for the expected range ofcoded data rates

[1231] set counter_flushed_too_earl_ymask=1 to enable this errorcondition to be detected

[1232] Two interrupt service routines are required:

[1233] Video Demux service to obtain the value of vbv delay for thefirst picture in each new stream

[1234] Counter flushed too early service to react to this condition

[1235] The video demux (also known as the video parser) can generate aninterrupt when it decodes the vbv_delay for a new video stream (i.e.,the first picture to arrive at the video demux after a FLUSH). Theinterrupt service routine should compute an appropriate value forbit_count_target and write it. When the bit counter reaches this target,it will insert an enable into a short queue between the bit counter andthe output gate. When the output gate opens it removes an enable fromthis queue.

[1236] A.12.6.1 Starting a New Stream Shortly After Another Finishes

[1237] As an example, the MPEG stream which is about to finish is calledA and the MPEG stream about to start is called B. A FLUSH Token shouldbe inserted after the end of A. This pushes the last of its coded datathrough the decoder and alerts the various sections of the decoder toexpect a new stream.

[1238] Normally, the bit counter will have reset to zero, A havingalready met its start-up conditions. After the FLUSH, the bit counterwill start counting the bits in stream B. When the Video Demux hasdecoded the vbv_delay from the first picture in stream B, an interruptwill be generated allowing the bit counter to be configured.

[1239] As the FLUSH marking the end of stream A passes through theoutput gate, the gate will close. The gate will remain closed until Bmeets its start-up conditions. Depending on a number of factors such as:the start-up delay for stream B and the depth of the buffers, it ispossible that B will have already met its start-up conditions when theoutput gate closes. In this case, there will be an enable waiting in thequeue and the output gate will immediately open. Otherwise, stream Bwill have to wait until it meets its start-up requirements.

[1240] A.12.6.2 A Succession of Short Streams

[1241] The capacity of the queue located between the bit counter and theoutput gate is sufficient to allow 3 separate video streams to have mettheir start-up conditions and to be waiting for a previous stream tofinish being decoded. In the present invention, this situation will onlyoccur if very short streams are being decoded or if the off-chip buffersare very large as compared to the picture format being decoded).

[1242] In FIG. 69 stream A is being decoded and the output gate isopen). Streams B and C have met their start-up conditions and areentirely contained within the buffers managed by the Spatial Decoder.Stream D is still arriving at the input of the Spatial Decoder.

[1243] Enables for streams B and C are-in the queue. So, when stream Ais completed B will be able to start immediately. Similarly C can followimmediately behind B.

[1244] If A is still passing through the output gate when D meets itsstart-up target an enable will be added to the queue, filling the queue.If no enables have been removed from the queue by the time the end of Dpasses the bit counter (i.e., A is still passing through the outputgate) no new stream will be able to start through the bit counter.Therefore, coded data will be held up at the input until A completes andan enable is removed from the queue as the output gate is opened toallow B to pass through.

[1245] A.12.7 Advanced Operation

[1246] In accordance with the present invention, advanced control of thestart-up logic allows user software to infinitely extend the length ofthe enable queue described in A.12.6, “Basic operation”. This level ofcontrol will only be required where the video decoder must accommodate aseries of short video streams longer than that described in A.12.6.2, ”A succession of short streams”.

[1247] In addition to the configuration required for Basic operation ofthe system, the following configurations are required after reset(having gained access to the start-up control logic by writing 1 tostartup access):

[1248] set offchip_queue=1

[1249] set accept_enable_mask=1 to enable interrupts then an enable hasbeen removed from the queue

[1250] set target_met_task=1 to enable interrupts when a stream's bitcount target is met

[1251] Two additional interrupt service routines are required:

[1252] accept enable interrupt

[1253] Target met interrupt

[1254] When a target met interrupt occurs, the service routine shouldadd an enable to its off-chip enable queue.

[1255] A.12.7.1 Output Gate Logic Behavior

[1256] Writing a 1 to the enable_stream register loads an enable into ashort queue.

[1257] When a FLUSH (marking the end of a stream) passes through theoutput gate the gate will close. If there is an enable available at theend of the queue, the gate will open and generate anaccept_enable_event. If accept_enable_mask is set to one, an interruptcan be generated and an enable is removed from the end of the queue (theregister enable_stream is reset).

[1258] However, if accept_enable_mask is set to zero, no interrupt isgenerated following the accept_enable_event and the enable is NOTremoved from the end of the queue. This mechanism can be used to keepthe output gate open as described in A.12.5.

[1259] A.12.8 Bit Counting

[1260] he bit counter starts counting after a FLUSH Token passes throughit. This FLUSH Token indicates the end of the current video stream. Inthis regard, the bit counter continues counting until it meets the bitcount target set in the bit_count_target register. A target met event isthen generated and the bit counter resets to zero and waits for the nextFLUSH Token.

[1261] The bit counter will also stop incrementing when it reaches itmaximum count (255).

[1262] A.12.9 Bit Count Prescale

[1263] In the present invention, 2^((bit) ^(_(—)) ^(count) ^(_(—))^(prescale+1))×512 bits are required to increment the bit counter once.Furthermore, bit_count_prescale is a 3 bit register than can hold avalue between 0 and 7. TABLE A.12.2 Example bit counter ranges n Range(bits) Resolution (bits) 0 0 to 252144 1024 1 0 to 524288 2048 7 0 to31457280 122880

[1264] The bit count is approximate, as some elements of the videostream will already have been Tokenized (e.g., the start codes) and,therefore includes non-data Tokens.

[1265] A.12.10 Counter Flushed Too Early

[1266] If a FLUSH token arrives at the bit counter before the bit counttarget is attained, an event is generated which can cause an interrupt(if counter_flushed_too_early_mask=1). If the interrupt is generated,then the bit counter circuit will stop, preventing further data input.It is the responsibility of the user's software to decide when to openthe output gate after this event has occurred. The output gate can bemade to open by writing 0 as the bit count target. These circumstancesshould only arise when trying to decode video streams that last only afew pictures.

[1267] Section A.13 Buffer Management

[1268] The Spatial Decoder manages two logical data buffers: the codeddata buffer (CDB) and the Token buffer (TB).

[1269] The CDB buffers coded data between the Start Code Detector andthe input of the Huffman decoder. This provides buffering for low datarate coded video data. The TB buffers data between the output of theHuffman decoder and the input of the spatial video decoding circuits(inverse modeler, quantizer and DCT). This second logical buffer allowsprocessing time to include a spread so as to accommodate processingpictures having varying amounts of data.

[1270] Both buffers are physically held in a single off-chip DRAM array.The addresses for these buffers are generated by the buffer manager.

[1271] A.13.1 Buffer Manager Registers

[1272] The Spatial Decoder buffer manager is intended to be configuredonce immediately after the device is reset. In normal operation, thereis no requirement to reconfigure the buffer manager. After reset isremoved from the Spatial Decoder, the buffer manager is halted (with itsaccess register, buffer_manager_access, set to 1) awaitingconfiguration. After the registers have been configured,buffer_manager_access can be set to 0 and decoding can commence.

[1273] Most of the registers used in the buffer manager cannot beaccessed reliably while the buffer manager is operating. Before any ofthe buffer manager registers are accessed buffer_manager_access must beset to 1. This makes it essential to observe the protocol of waitinguntil the value 1 can be read from buffer_manager_access. The time takento obtain and release access should be taken into consideration whenpolling such registers as cdb_full and cdb_empty to monitor bufferconditions. TABLE A.13.1 Buffer manager registers Register nameSize/Dif. Reset State Description buffer_manager_access  1 1 This accessbit stops the operation of the buffer manager so that is rw variousregisters can be accessed reliably. See A.5.4.1 Note: this accessregister is unusual as its default state after reset s 1 i.e. afterreset the buffer manager is halted awaiting configuration via themicroprocessor interface. buffer_manager_keyhole_address  6 x Keyholeaccess to the extended address space used for the buffer rw managerregisters shown below. See A.5.4.3 for more buffer_manager_keyhole_data 8 x information about accessing registers through a keyhole. rwbuffer_limit 18 x This specifies the overall size of the $$ rw SpatialDecoder. All buffer addresses are $$ this $$ size and so will wrap roundwithin the $$ provided cdb_base 18 x These registers point to the baseof the $$ data (cdb) and Token tb_base rw (tb) buffers. cdb_length 18 xThese registers specify the length (i.e. size) of the coded data (cdb)tb_length rw and Token (tb) buffers. cdb_read 18 x These registers holdan offset from the buffer base and indicate tb_read ro where data willbe read from next. cdb_number 18 x These registers show how much data iscurrently held in the buffer tb_number ro cdb_full  1 x These registerswill be set to 1 if the coded data (cdb) or $$ tb_full ro $$ cdb_empty 1 x $$ registers will be set to 1 if the coded data (cdb) or Tokentb_empty ro buffer empties.

[1274] A.13.1 Bluffer Manager Pointer Values

[1275] Typically, data is transferred between the Spatial Decoder andthe off_chip DRAM in 64 byte bursts (using the DRAM's fast page mode).All the buffer pointers and length registers refer to these 64 byte (512bit) blocks of data. So, the buffer manager's 18 bit registers describea 256 k block linear address space (i.e., 128 Mb).

[1276] The 64 byte transfer is independent of the width (8, 16 or 32bits) of the DRAM interface.

[1277] A.13.2 Use of the Buffer Manager Registers

[1278] The Spatial Decoder buffer manager has two sets of registers thatdefine two similar buffers. The buffer limit register (buffer_limit)defines the physical upper limit of the memory space. All addresses arecalculated modulo this number.

[1279] Within the limits of the available memory, the extent of eachbuffer is defined by two registers: the buffer base (cdb_base andtb_base) and the buffer length (cdb_length and tb_length). All theregisters described thus far must be configured before the buffers canbe used.

[1280] The current status of each buffer is visible in 4 registers. Thebuffer read register (cdb_read and tb_read) indicates an offset from thebuffer base from which data will be read next. The buffer numberregisters (cdb_number and tb_number) indicate the amount of datacurrently held by buffers. The status bits cdb_full, tb_full, cdb_emptyand tb_empty indicate if the buffers are full or empty.

[1281] As stated in A.13.1.1, the unit for all the above mentionedregisters is a 512 bit block of data. Accordingly, the value-read fromcdb_number should be multiplied by 512 to obtain the number of bits inthe coded data cuffer.

[1282] A.13.3 Zero Buffers

[1283] Still picture applications (e.g., using JPEG) that do not have a“real-time” requirement will not need the large off-chip bufferssupported by the buffer manager. In this case, the DRAM interface can beconfigured (by writing 1 to the zero_buffers register) to ignore thebuffer manager to provide a 128 bit stream on-chip FIFO for the codeddata buffer and the Token buffers.

[1284] The zero buffers option may also be appropriate for applicationswhich operate working at low data rates and with small picture formats.

[1285] Note: the zero_buffers register is part of the DRAM interfaceand, therefore, should be set only during the post-reset configurationof the DRAM interface.

[1286] A.13.4 Buffer Operation

[1287] The data transfer through the buffers is controlled by ahandshake Protocol. Hence, it is guaranteed that no data errors willoccur if the buffer fills or empties. If a buffer is filled, then thecircuits trying to send data to the buffer will be halted until there isspace in the buffer. If a buffer continues to be full, more processingstages “up steam” of the buffer will halt until the Spatial Decoder isunable to accept data on its input port. Similarly, if a buffer empties,then the circuits trying to remove data from the buffer will halt untildata is available.

[1288] As described in A.13.2, the position and size of the coded dataand Token buffer are specified by the buffer base and length registers.The user is responsible for configuring these registers and for ensuringthat there is no conflict in memory usage between the two buffers.

[1289] Section A.14 Video Demux

[1290] The Video Demux or Video parser as it is also called, completesthe task of converting coded data into Tokens started by the Start CodeDetector. There are four main processing blocks in the Video Demux:Parser State Machine, Huffman decoder (includincg an ITOD), Macroblockcounter and ALU.

[1291] The Parser or state machine follows the syntax of the coded videodata and instructs the other units. The Huffman decoder convertsvariable length coded (VLC) data into integers. The Macroblock counterkeeps track of which section of a picture is being decoded. The ALUperforms the necessary arithmetic calculations.

[1292] A.14.1 Video Demux Registers TABLE A.14.1 Top level Video Demuxregisters Register name Size/Dif. Reset State Description demux_access 1 0 This access bit stops the operation of the Video Demux so that $$CED_H_CTRL(7) rw various registers can be accessed reliably. See A.6.4.1huffman_error_code  3 When the Video Demux stops following thegeneration of a CED_H_CTRL(5.4) ro huffman_event interrupt request this3 bit register holds a value indicating why the interrupt was generated.See A.14.5.1 parser_error_code  8 When the Video Demux stops followingthe generation of a parser_event CED_H_DMUX_ERR ro interrupt requestthis 8 bit register holds a value indicating why the interrupt wasgenerated. See A.14.5.2 demux_keyhole_address 12 x Keyhole access to theVideo Demux's extended address space. See CED_H_KEYHOLE_ADDR rw A.6.4.3for more information about accessing registers demux_keyhole_data  8 xthrough a keyhole. CED_H_KEYHOLE rw Tables A.14.2, A.14.3 and A.14.4describe the registers that can be accessed via the keyhole.dummy_last_picture  1 0 When this register is set to 1 the Video Demuxwill generate information CED_H_ALU_REG0 rw for a “dummy” intra pictureas the last picture of an MPEG sequence. r_rom_control This function isuseful when the Temporal Decoder is configured forr_dummy_last_frame_bit automatic picture re-ordering (see A.18.3.5.“Picture sequence re- ordering”. to flush the last P or $$ picture outof the Temporal Decoder. No “dummy” picture is required if: the TemporalDecoder is not configured for re-ordering another MPEG sequence will bedecoded immediately (as this will also flush out the last picture) thecoding standard is not MPEG field_info  1 0 When this register is set to1 the first byte of any MPEG CED_H_ALU_REG0 rw extra_information_pictureis placed in the FIELD_INFO Token. See r_rom_control A.14.7.1r_field_info_bit continue  1 0 This register allows user software tocontrol how much extra. user or CED_H_ALU_REG0 rw extension data itwants to receive when is it is detected by the decoder. r_rom_controlSee A.14.6 and A.14.7 r_continue_bit rom_revision  8 Immediatelyfollowing reset this holds a copy of the microcode RCM CED_H_ALU_REG1 rorevision number. r_rom_revision This register is also used to present tocontrol software data values read from the coded data. See A.14.6,“Receiving User and Extension data”. and A.14.7. “Receiving Extrainformation”, Huffman_event  1 0 A Huffman event is generated if anerror is found in the coded data. See rw A.14.5.1 for a description ofthese events. Huffman_mask  1 0 If the mask register is set to 1 then aninterrupt can be generated and the rw Video Demux will stop. If the maskregister is set to 0 then no interrupt is generated and the Video Demuxwill attempt to recover from the error. parser_event  1 0 A Parser eventcan be in response to errors in the coded data or to the rw arrival ofinformation at the Video Demux that requires software parser_mask  1 0intervention. See A.14.5.2 for a description of these events. rw If themask register is set to 1 then an interrupt can be generated and theVideo Demux will stop. If the mask register is set to 0 then nointerrupt is generated and the Video Demux will attempt to continue.

[1293] TABLE A.14.2 Video demux picture construction registers Registername Size/Dir. Reset State Description component_name_0 8 x During JPEGoperation the register component_name_n holds an 8 bit valuecomponent_name_1 rw indicating (to an application) which colourcomponent has the component ID n. component_name_2 component_name_3horiz_pels 16  x These registers hold the horizontal and verticaldimensions of the video being rw decoded in pixels. vert_pels 16  x Seesection A 14.2 rw horiz_macroblocks 16  x These registers hold thehorizontal and vertical dimensions of the video being rw decoded inmacroblocks. vert_macroblocks 16  x See section A 14.2 rw max_n 2 xThese registers hold the macroblock width and height in blocks (8 × 8pixels). rw The values 0 to 3 indicate a width/height of 1 to 4 blocks.max_v 2 x See section A.14.2 rw max_component_id 2 x The values 0 to 3indicate that 1 to 4 different video components are currently rw beingdecoded. See section A.14.2 Nf 8 x During JPEG operation this registerholds the parameter Nf (number of image rw components in frame).blocks_h_0 2 x For each of the 4 colour components the registersblocks_h_n and blocks_h_1 rw blocks_v_n hold the number of blockshorizontally and vertically in a blocks_h_2 macroblock for the colourcomponent with component ID n. blocks_h_3 See section A.14.2 blocks_v_02 x blocks_v_1 rw blocks_v_2 blocks_v_3 tq_0 2 x The two bit value heldby the register tq_n describes which inverse tq_1 rw Quantisation tableis to be used when decoding data with component ID n. tq_2 tq_3

[1294] A14.14-1 Register Loading and Token Generation

[1295] Many of the registers in the Video Demux hold values that relatedirectly to parameters normally communicated in the coded picture/videodata. For example, the horiz_pels register corresponds to the MPEGsequence header information, horizontal_size, and the JPEG frame headerparameter, X. These registers are loaded by the Video Demux when theappropriate coded data is decoded. These registers are also associatedwith a Token. For example, the register, horiz_pels, is associated withToken, HORIZONTAL_SIZE. The Token is generated by the Video Demux when(or soon after) the coded data is decoded. The Token can also besupplied directly to the input of the Spatial Decoder. In this case, thevalue carried by the Token will configure the Video Demux registerassociated with it. TABLE A.14.3 Video demux Huffman table registersRegister name Size/Dif. Reset State Description dc_huff_0 2 The two bitvalue held by the register dc_huff_n describes which Huffman dc_huff_1rw decoding table is to be used when decoding the DC coefficients ofdata with dc_huff_2 component ID n. dc_huff_3 Similarly ac_huff_ndescribes the table to be used when decoding AC ac_huff_0 2coefficients. ac_huff_1 rw Baseline JPEG requires up to two Huffmantables per scan. The only tables ac_huff_2 implemented are 0 and 1.ac_huff_3 dc_bits_0[15:0] 8 Each of these is a table of 16, eight bitvalues. They provide the BITS dc_bits_1[15:0] rw information (see JPEGHuffman table specification) which form part of the ac_bits_0[15:0] 8description of two DC and two AC Huffman tables. ac_bits_1[15:0] rw Seesection A.14.3.1 dc_huffval_0[11:0] 8 Each of these is table of 12.eight bit values. They provide the HUFFVAL dc_huffval_1[11:0] rwinformation (see JPEG Huffman table specification) which form part ofthe description of two DC Huffman tables. See section A.14.3.1ac_huffval_0[161:0] 8 Each of these is a table of 152, eight bit values.They provide the HUFFVAL ac_huffval_1[161:0] rw information (see JPEGHuffman table specification) which form part of the description of twoAC Huffman tables. See section A.14.3.1 dc_zssss_0 8 These 8 bitregisters hold values that are “special cased” to accelerate thedc_zssss_1 rw decoding of certain frequently used JPEG VLCs. ac_eob_0 8dc_ssss —magnitude of DC coefficient is 0. ac_eob_1 rw ac_eob - end ofblock ac_zrl_0 8 ac_zrl - run of 16 zeros ac_zrl_1 rw

[1296] TABLE A.14.4 Other Video Demux registers Register name Size/Dir.Reset State Description buffer_size 10 This register is loaded whendecoding MPEG data with a value indicating the rw size of VBV bufferrequired in an ideal decoder. This value is not used by the decoderchips. However, the value it holds may be useful to user software whenconfiguring the coded data buffer size and to determine whether thedecoder is capable of decoding a particular MPEG data file. pel_aspect 4This register is loaded when decoding MPEG data with a value indicatingthe rw pel aspect ratio. The value is a 4 bit integer that is used as anindex into a table defined by MPEG. See the MPEG standard for adefinition of this table. This value is not used by the decoder chips.However, the value it holds may be useful to user software whenconfiguring a display or output device. bit_rate 18 This register isloaded when decoding MPEG data with a value indicating the rw coded datarate. See the MPEG standard for a definition of this value. This valueis not used by the decoder chips. However, the value it holds may beuseful to user software when configuring the decoder start-up registers.pic_rate 4 This register is loaded when decoding MPEG data with a valueindicating the rw picture rate. See the MPEG standard for a definitionof this value. This value is not used by the decoder chips. However, thevalue it holds may be useful to user software when configuring a displayor output device. constrained t This register is loaded when decodingMPEG data to indicate if the coded data rw meets MPEG's constrainedparameters. See the MPEG standard for a definition of this flag. Thisvalue is not used by the decoder chips. However, the value it holds maybe useful to user software to determine whether the decoder is capableof decoding a particular MPEG data file. picture_type 2 During MPEGoperation this register holds the picture type of the picture being rwdecoded. h_251_pic_type 8 This register is loaded when decoding H.251data. It holds information about rw the picture format.

Flags: s - Split Screen Indicator d - Document Camera f - Freeze PictureRelease This value is not used by the decoder chips. However, theinformation should be used when configuring horiz_pels, vert_pels andthe display or output device. broken_closed 2 During MPEG operation thisregister holds the broken_link and closed_gop rw information for thegroup of pictures being decoded.

Flags: c - closed_gop prediction_mode 5 During MPEG and H.261 operationthis register holds the current value of rw prediction mode.

Flags: h - enable K.261 loop filter y - reset backward vector predictionvbv_delay 16 This register is loaded when decoding MPEG data with avalue indicating the rw minimum start-up delay before decoding shouldstart. See the MPEG standard for a definition of this value. This valueis not used by the decoder chips. However, the value it holds may beuseful to user software when configuring the decoder start-up registers.pic_number 8 This register holds the picture number for the picturesthat is currently being rw decoded by the Video Demux. This number wasgenerated by the start code detector when this picture arrived there.See Table A.11.2 for a description of the picture number.dummy_last_picture 1 0 These registers are also visible at the toplevel. See Table A.14.1 rw field_info 1 0 rw continue 1 0 rwrom_revision 8 rw coding_standard 2 This register is loaded by theCODING_STANDARD Token to configure ro the Video Demux's mode ofoperation. See section A.21.1 restart_interval 8 This register is loadedwhen decoding JPEG data with a value indicating the rw minimum start-updelay before decoding should start. See the MPEG standard for adefinition of this value.

[1297] TABLE A.14.5 Register to Token cross reference register Tokenstandard comment component_name_n COMPONENT_NAME JPEG in coded data.MPEG not used in standard. H.261 horiz_pels HORIZONTAL_SIZE MPEG incoded data. vert_pels VERTICAL_SIZE JPEG H.261 automatically derivedfrom picture type. horiz_macroblocks HORIZONTAL_MBS MPEG controlsoftware must derive from vert_macroblocks VERTICAL_MBS JPEG horizontaland vertical picture size H.261 automatically derived from picture type.max_h DEFINE_MAX_SAMPLING MPEG control software must configure. max_vSampling structure is fixed by standard. JPEG in coded data. H.251automatically configured for 4.2.0 video. max_component_id MAX_COMP_IDMPEG control software must configure. Sampling structure is fixed bystandard. JPEG in coded data. H.261 automatically configured for 4.2.0video. tq_0 JPEG_TABLE_SELECT JPEG in coded data. tq_1 MPEG not used instandard. tq_2 H.261 tq_3 blocks_h_0 DEFINE_SAMPLING MPEG controlsoftware must configure. blocks_h_1 Sampling structure is fixed byblocks_h_2 standard. blocks_h_3 JPEG in coded data. blocks_v_0 H.261automatically configured for 4.2.0 blocks_v_1 video. blocks_v_2blocks_v_3 dc_huff_0 in scan header data JPEG in coded data. dc_huff_1MPEG_DCH_TABLE MPEG control software must configure. dc_huff_2 H.261 notused in standard. dc_huff_3 ac_huff_0 in scan header data JPEG in codeddata. ac_huff_1 MPEG not used in standard. ac_huff_2 H.261 ac_huff_3dc_bits_0[15:0] in DATAToken following JPEG in coded data.dc_bits_1[15:0] DHT_MARKER Token dc_huffval_0[11:0] MPEG controlsoftware must configure. dc_huffval_1[11:0] H.251 not used in standard.dc_zssss_0 dc_zssss_1 ac_bits_0[15:0] in DATAToken following JPEG incoded data. ac_bits_1[15:0] DHT_MARKER Token ac_huffval_0[161:0] MPEGnot used in standard. ac_huffval_1[161:0] H.261 ac_eob_0 ac_eob_1ac_zrl_0 ac_zrl_1 buffer_size VBV_BUFFER_SIZE MPEG in coded data. JPEGnot used in standard H.261 pel_aspect PEL_ASPECT MPEG in coded data.JPEG not use in standard H.261 bit_rate BIT_RATE MPEG in coded data.JPEG not used in standard H.261 pic_rate PICTURE_RATE MPEG in codeddata. JPEG not used in standard H.261 constrained CONSTRAINED MPEG incoded data. JPEG not used in standard H.261 picture_type PICTURE_TYPEMPEG in coded data JPEG not used in standard H.261 broken_closedBROKEN_CLOSED MPEG in coded data. JPEG not used in standard H.261prediction_mode PREDICTION_MODE MPEG in coded data. JPEG not used instandard H.261 h_261_pic_type PICTURE_TYPE MPEG not relevant (whenstandard is H.261) JPEG H.261 in coded data. vbv_delay VBV_DELAY MPEG incoded data. JPEG not used in standard H.261 pic_number Carried by: MPEGGenerated by start code detector. PICTURE_START JPEG H.261coding_standard CODING_STANDARD MPEG configured in start code by controlJPEG software detector. H.261

[1298] A.14.2 Picture Structure

[1299] In the present invention, picture dimensions are described to theSpatial Decoder in 2 different units: pixels and macroblocks. JPEG andMPEG both communicate picture dimensions in pixels. Communicating thedimensions in pixels determine the area of the buffer that contains thevalid data; this may be smaller than the total buffer size.Communicating dimensions in macroblocks determines the size of bufferrequired by the decoder. The macroblock dimensions must be derived bythe user from the pixel dimensions. The Spatial Decoder registersassociated with this information are: horiz_pels, vert_pels,horiz_macroblocks and vert_macroblocks.

[1300] The Spatial Decoder registers, blocks_h_n, blocks_v_n, max_h,max_v and max_component_id specify the composition of the macroblocks(minimum coding units in JPEG). Each is a 2 bit register than can holdvalues in the range 0 to 3. All except max_component_id specify a blockcount of 1 to 4. For example, if register max_h holds 1, then amacroblock is two blocks wide. Similarly, max_component_id specifies thenumber of different color components involved. TABLE A.14.6Configuration for various macroblock formats 2:1:1 4:2:2 4:2:0 1:1:1max_h 1 1 1 0 max_v 0 1 1 0 max_component_id 2 2 2 2 blocks_h_0 1 1 1 0blocks_h_1 0 0 0 0 blocks_h_2 0 0 0 0 blocks_h_3 x x x x blocks_v_0 0 11 0 blocks_v_1 0 1 0 0 blocks_v_2 0 1 0 0 blocks_v_3 x x x x

[1301] A.14.7 Huffman Tables

[1302] A.14.3.1 JPEG Style Huffman Table Descriptions

[1303] In the invention, Huffman table descriptions are provided to theSpatial decoder via the format used by JPEG to communicate tabledescriptions between encoders and decoders. There are two elements toeach table description: BITS and HUFFVAL. For a full description of howtables are encoded, the user is directed to the JPEG specification.

[1304] A.14.3.1.1 Bits

[1305] BITS is a table of values that describes how many differentsymbols are encoded with each length of VLC. Each entry is an 8 bitvalue. JPEG permits VLCs with up to 16 bits long, so there are 16entries in each table.

[1306] The BITS[0] describes how many different 1 bit VLCs exist whileBITS[1] describes how many different 2 bit VLCs exist and so forth.

[1307] A.14.3.1.2 HUFFVAL

[1308] HUFFVAL is table of 8 bit data values arranged in order ofincreasing VLC length. The size of this table will depend on the numberof different symbols that can be encoded by the VLC.

[1309] The JPEG specification describes in further detail how Huffmancoding tables can be encoded or decoded into this format.

[1310] A.14.3.1.3 Configuration by Tokens

[1311] In a JPEG bitstream, the DHT marker precedes the description ofthe Huffman tables used to code AC and DC coefficients. When the StartCode Detector recognizes a DHT marker, it generates a DHT_MARKER Tokenand places the Huffran table description in the following DATA Token(see A.11.3.4).

[1312] Configuration of AC and DC coefficient Huffman tables within theSpatial Decoder can be achieved by supplying

[1313] DATA and DHT_MARKER Tokens to the input of the Spatial Decoderwhile the Spatial Decoder is configured for JPEG operation. Thismechanism can be used for configuring the DC coefficient Huffman tablesrequired for MPEG operation, however, the codinq standard of the SpatialDecoder must be set to JPEG while the tables are down loaded. TABLEA.14.7 Huffman table configuration via Tokens E 7 6 5 4 3 2 1 0 TokenName 1 0 0 0 1 0 1 0 1 CODING_STANDARD 0 0 0 0 0 0 0 0 1 1 = JPEG 0 0 00 1 1 1 0 0 DHT_MARKER 1 0 0 0 0 0 1 x x DATA 1 t t t t t t t t T_(n) -Value indicating which Huffman table is to be loaded. JPEG allows 4 Thissequence can be repeated tables to be downloaded. to allow severaltables to be Values 0x00 and 0x01 specify DC coefficient coding tables 0and 1 downloaded in a single Token Values 0x10 and 0x11 specifies ACcoefficient coding tables 0 and 1 1 n n n n n n n n L_(i) - 16 wordscarrying BITS information 1 n n n n n n n n 1 n n n n n n n n V_(ij) -Words carrying HUFFVAL information (the number of words depends on thenumber of different e n n n n n n n n symbols). e - the extension bitwill be 0 if this is the end of the DATA Token or 1 if another tabledescription is contained in the same DATA Token.

[1314] A.14.3.1.4 Configuration by MPI

[1315] The AC and DC coefficient Huffman tables can also be writtendirectly to registers via the MPI. See Table A.14.3.

[1316] The registers dc_bits0[15:0] and dc_bits1[15:0]hold the BITSvalues for tables 0x00 and 0x01.

[1317] The registers ac_bits_(—)0[15:0] and ac_bits_(—)1 [15:0] hold theBITS values for tables 0x10 and 0x11.

[1318] The registers dc_huffval_(—)0[11:0] and dc_huffval_(—)1[11:0]hold the HUFFVAL values for tables 0x00 and 0x01.

[1319] The registers ac_huffval_(—)0[161:0] and ac_huffval_(—)1[161:0]hold the HUFFVAL values for tables 0x10 and 0x11.

[1320] A.14.4 Configuring for Different Standards

[1321] The Video Demux supports the requirements of MPEG, JPEG andH.261. The coding standard is configured automatically by theCODING_STANDARD Token generated by the Start Code Detector.

[1322] A.14.4.1 H.261 Huffman Tables

[1323] All the Huffman tables required to decode H.261 are held in ROMswithin the Spatial Decoder and more particular in the parser statemachine of the Video demux and, therefore require no user intervention.

[1324] A.14.4.2 H.261 Picture Structure

[1325] H.261 is defined as supporting only two picture formats: CIF andQCIF. The picture format in use is signalled in the PTYPE section of thebitstream. When this data is decoded by the Spatial Decoder, it isplaced in the h_(—)261_pic_type registers and the PICTURE_TYPE Token. Inaddition, all the picture and macroblock construction registers areconfigured automatically.

[1326] The information in the various registers is also placed intotheir related Tokens (see Table A.14.5), and this ensures that otherdecoder chips (such as the Temporal Decoder) are correctly configured.

[1327] A.14.4.3 MPEG Huffman Tables

[1328] The majority of the Huffman coding tables required to decode MPEGare held in ROMs within the Spatial Decoder (again, in the parser statemachine) and, thus, require no user intervention. The exceptions are thetables required for decoding the DC coefficients of Intral macroblocks.Two tables are required, one for chroma the other for luma. These mustbe configured by user software before decoding begins. TABLE A.14.8Automatic settings for H.261 CIF/ macroblock construction OCIF pictureconstruction CIF OCIF max_h 1 horiz_pels 352 176 max_v 1 vert_pels 288144 max_component_id 2 horiz_macroblocks 22 11 blocks_h_0 1vert_macroblocks 18 9 blocks_h_1 0 blocks_h_2 0 blocks_v_0 1 blocks_v_10 blocks_v_2 0

[1329] Table A.14.10 shows the sequence of Tokens required to configurethe DC coefficient Huffman tables within the Spatial Decoder.Alternatively, the same results can be obtained by writing thisinformation to registers via the MPI.

[1330] The registers dc_huff_n control which DC coefficient Huffmantables are used with each color component. Table A.14.9 shows how theyshould be configured for MPEG operation. This can be done directly viathe MPI or by using the MPEG_DCH_TABLE Token. TABLE A.14.9 MPEG DCHuffman table selection via MPI dc_huff_0 0 dc_huff_1 1 dc_huff_2 1dc_huff_3 x

[1331] TABLE A.14.10 MPEG DC Huffman table configuration E [7:0] TokenName 1 0x15 CODING_STANDARD 0 0x01 1 = JPEG 0 0x1C DHT_MARKER 1 0x04DATA (could be any colour component. 0 is used in this example) 1 0x00 0indicates that this Huffman table is DC coefficient coding table 0 10x00 16 words carrying BITS information describing a total of 9 1 0x02different VLCs: 1 0x03 1 0x01 2.2 bit codes 1 0x01 3.3 bit codes 1 0x011.4 bit codes 1 0x01 1.5 bit codes 1 0x00 1.6 bit codes 1 0x00 1.7 bitcodes 1 0x00 1 0x00 If configuring via the MPI rather than 1 0x00 withTokens these values would be 1 0x00 written into the dc_bits_0[15:0]registers. 1 0x00 1 0x00 1 0x00 1 0x01 9 words carrying HUFFVALinformation 1 0x02 If configuring via the MPI rather than 1 0x00 withTokens these values would be 1 0x03 written into the dc_huttval_0[11:0]registers. 1 0x04 1 0x05 1 0x06 1 0x07 0 0x08 0 0x1C DHT_MARKER 1 0x04DATA (could be any colour component, 0 is used in this example) 1 0x01 1indicates that this Huffman table is DC coefficient coding table 1 10x00 16 words carrying BITS information describing a total of 9 1 0x03different VLCs: 1 0x01 3.2 bit codes 1 0x01 1.3 bit codes 1 0x01 1.4 bitcodes 1 0x01 1.5 bit codes 1 0x01 1.6 bit codes 1 0x01 1.7 bit codes 10x00 1.8 bit codes 1 0x00 1 0x00 1 0x00 If configuring via the MPIrather than 1 0x00 with Tokens these values would be 1 0x00 written intothe dc_bits_1[15:0] registers. 1 0x00 1 0x00 1 0x00 9 words carryingHUFFVAL information 1 0x01 If configuring via the MPI rather than 1 0x02with Tokens these values would be 1 0x03 written into thedc_huffval_1[11:0] registers. 1 0x04 1 0x05 1 0x06 1 0x07 0 0x08 1 0x04MPEG_DCH_TABLE 0 0x00 Configure so table 0 is used for component 0 10x05 MPEG_DCH_TABLE 0 0x01 Configure so table 1 is used for component 11 0x06 MPEG_DCH_TABLE 0 0x01 Configure so table 1 is used for component2 1 0x15 CODING_STANDARD 0 0x02 2 = JPEG

[1332] A.14.4.4 MPEG Picture Structure

[1333] The macroblock construction defined for MPEG is the same as thatused by H.261. The picture dimensions are encoded in the coded data.

[1334] For standard 4:2:0 operation, the macroblock characteristicsshould be configured as indicated in Table A.14.8. This can be doneeither by writing to the registers as indicated or by applying theequivalent Tokens (see Table A.14.5) to the input of the SpatialDecoder.

[1335] The approach taken to configure picture dimensions will dependupon the application. If the picture format is known before decodingstarts, then the picture construction registers listed in Table A.14.8can be initialized with appropriate values. Alternatively, the picturedimensions can be decoded from the coded data and used to configure theSpatial Decoder. In this case the user must service the parser errorERR_MPEG_SEQUENCE, see A.14.8, ” Changes at the MPEG sequence layer”.

[1336] A.14.4.5 JPEG

[1337] Within baseline JPEG, there are a number of encoder options thatsignificantly alter the complexity of the control software required tooperate the decoder. In general, the Spatial Decoder has been designedso that the required support is minimal where the following condition ismet:

Number of color components per frame is less than 5(N_(f)≦4)

[1338] A.14.4.6 JPEG Huffman Tables

[1339] Furthermore, JPEG allows Huffman coding tables to be down loadedto the decoder. These tables are used when decoding the VLCs describingthe coefficients. Two tables are permitted per scan for decoding DCcoefficients and two for the AC coefficients.

[1340] There are three different types of JPEG file: Interchange format,an abbreviated format for compressed image data, and an abbreviatedformat for table data. In an interchange format file there is bothcompressed image data and a definition of all the tables (Huffman,Quantization etc.) required to decode the image data. The abbreviatedimage data format file omits the table definitions. The abbreviatedtable format file only contains the table definitions.

[1341] The Spatial Decoder will accept all three formats. However,abbreviated image data files can only be decoded if all the requiredtables have been defined. This definition can be done via either of theother two JPEG file types, or alternatively, the tables could be set-upby user software.

[1342] If each scan uses a different set of Huffman tables, then thetable definitions are placed (by the encoder) in the coded data beforeeach scan. These are automatically loaded by the Spatial Decoder for useduring this and any subsequent scans.

[1343] To improve the performance of the Huffman decoding, certaincommonly used symbols are specially cased. These are: DC coefficientwith magnitude 0, end of block AC coefficients and run of 16 zero ACcoefficients. The values for these special cases should be written intothe appropriate registers.

[1344] A.14.4.6.1 Table Selection

[1345] The registers dc_huff_n and ac_huff_n control which AC and DCcoefficient Huffman tables are used with which color component. DuringJPEG operation, these relationships are defined by the TD_(j) and Ta_(j)fields of the scan header syntax.

[1346] A.14.4.7 JPEG Picture Structure

[1347] There are two distinct levels of baseline JPEG decoding supportedby the Spatial Decoder: up to 4 components per frame (N_(f)≦4) andgreater than 4 components per frame (N_(f)>4). If N_(f)>4 is used, thecontrol software required becomes more complex.

[1348] A.14.4.7.1 Nf≦4

[1349] The frame component specification parameters contained in theJPEG frame header configure the macroblock construction registers (seeTable A.14.8) when they are decoded. No user intervention is required,as all the specifications required to decode the 4 different colorcomponents as defined.

[1350] For further details of the options provided by JPEG the readershould study the JPEG specification. Also, there is a short descriptionof JPEG picture formats in § A.16.1.

[1351] A.14.4.7.2 JPEG with More Than 4 Components

[1352] The Spatial Decoder can decode JPEG files containing up to 256different color components (the maximum permitted by JPEG). However,additional user intervention is required if more than 4 color componentare to be decoded. JPEG only allows a maximum of 4 components in anyscan. only allows a maximum of 4 components in any scan.

[1353] A.14.4.8 Non-standard Variants

[1354] As stated above, the Spatial Decoder supports some pictureformats beyond those defined by JPEG and MPEG.

[1355] JPEG limits minimum coding units so that they contain no morethan 10 blocks per scan. This limit does not apply to the SpatialDecoder since it can process any minimum coding unit that can bedescribed by blocks_h_n, blocks_v_n, max_h and max_v.

[1356] MPEG is only defined for 4:2:0 macroblocks (see Table A.148).However, the Spatial Decoder can process three other componentmacroblock structures, (e.g., 4:2:2.

[1357] A.14.5 Video Events and Errors

[1358] The Video Demux can generate two types of events: parser eventsand Huffman events. See A.6.3, “Interrupts”, for a description of how tohandle events and interrupts.

[1359] A.14.5.1 Huffman Events

[1360] Huffman events are generated by the Huffman decoder. The eventwhich is indicated in huffman_event and huffman_mask determines whetheran interrupt is generated. If huffman_mask is set to 1, an interruptwill be generated and the Huffman decoder will halt. The registerhuffman_error_code[2:0] will hold a value indicating the cause of theevent.

[1361] If 1 is written to huffman_event after servicing the interrupt,the Huffman decoder will attempt to recover from the error. Also, ifhuffman_mask was set to 0 (masking the interrupt and not halting theHuffman decoder) the Huffman decoder will attempt to recover from theerror automatically.

[1362] A.14.5.2 Parser Events

[1363] Parser events are generated by the Parser. The event is indicatedin parser_event. Thereafter, parser_mask determines whether an interruptis generated. If parser_mask is set to 1, an interrupt will be generatedand the Parser will halt. The register parser_error_coder7:0] will holda value indicating the cause of event.

[1364] If 1 is written to huffman_event after servicing the interrupt,the Huffman decoder will attempt to recover from the error. Also, ifhuffman_mask was set to 0 (masking the interrupt and not halting theHuffman decoder) the Huffman decoder will attempt to recover form theerror automatically.

[1365] If 1 is written to parser event after servicing the interrupt,the Parser will start operation again. If the event indicated abitstream error, the Video Demux will attempt to recover from the error.

[1366] If parser_mask was set to 0, the Parser will set its event bit,but will not generate an interrupt or halt. It will continue operationand attempt to recover from the error automatically. TABLE A.14.11Huffman error codes huffman_error_code [2] [1] [0] Description 0 0 0 Noerror. This error should not occur during normal operation. x 0 1 Failedto find terminal code in VLC within 16 bits. x 1 0 Found serial datawhen Token expected x 1 1 Found Token when serial data expected 1 x xInformation describing more than 64 coefficients for a single block wasdecoded indicating a bitstream error. The block output by the VideoDemux will contain only 64 coefficients.

[1367] TABLE A.14.12 Parser error codes parser_error_code[7:0]Description 0x00 ERR_NO_ERROR No Parser error has occured, this eventshould not occur during normal operation 0x10 ERR_EXTENSION_TOKEN AnEXTENSION_DATA Token has been detected by the Parser. The detection ofthis Token should preceed a DATA Token that contains the extension data.See A 14.6 0x11 ERR_EXTENSION_DATA Following the detection of anEXTENSION_DATA Token, a DATA Token containing the extension data hasbeen detedcted. See A.14.6 0x12 ERR_USER_TOKEN A USER_DATA Token hasbeen detected by the Parser. The detection of this Token should preceeda DATA Token that contains the user data. See A.14.6 0x13 ERR_USER_DATAFollowing the detection of a USER_DATA Token, a DATA Token containingthe user data has been detedcted. See A.14.6 0x20 ERR_PSPARE H.261 PSAREinformation has been detected see A.14.7 0x21 ERR_GSPARE H.261 GSAREinformation has been detected see A.14.7 0x22 ERR_PTYPE The value of theH.251 picture type has changed. The register h_261_pic_type can beinspected to see what the new value is 0x30 ERR_JPEG_FRAME 0x31ERR_JPEG_FRAME_LAST 0x32 ERR_JPEG_SCAN Picture size or Ns changed 0x33ERR_JPEG_SCAN_COMP Component Change ! 0x34 ERR_DNL_MARKER 0x40ERR_MPEG_SEQUENCE One of the parameters communicated in the MPEGsequence layer has changed. See A.14.8 0x41 ERR_EXTRA_PICTURE MPEGextra_information_picture has been detected see A.14.7 0x42ERR_EXTRA_SLICE MPEG extra_information_since has been detected seeA.14.7 0x43 ERR_VBV_DELAY The VBV_DELAY parameter for the first picturein a new MPEG video sequence has been detected by the Video Demux. Thenew value of delay is available in the register vbv_delay. The firstpicture of a new sequence is defined as the first picture after asequence end. FLUSH or reset. 0x80 ERR_SHORT_TOKEN An incorrectly formedToken has been detected. This error should not occur during normaloperation. 0x90 ERR_H261_PIC_END_UNEXPECTED During H.261 operation theend of a picture has been encountered at an unexpected position. This islikely to indicate an error in the coded data. 0x91 ERR_GN_BACKUP DuringH.251 operation a group of blocks has been encountered with a groupnumber less than that expected. This is likely to indicate an error inthe coded data 0x92 ERR_GN_SKIP_GOB During H.261 operation a group ofblocks has been encountered with a group number greater than thatexpected. This is likely to indicate an error in the coded data. 0xA0ERR_NBASE_TAB During JPEG operation there has been an attempt to download a Huffman table that is not supported by baseline JPEG (baselineJPEG only supports tables 0 and 1 for entropy coding). 0xA1ERR_QUANT_PRECISION During JPEG operation there has been an attempt todown load a quantisation table that is not supported by baseline JPEG(baseline JPEG only supports 8 bit precision in quantisation tables).0xA2 ERR_SAMPLE_PRECISION During JPEG operation there has been anattempt to specify a sample precision greater than that supported bybaseline JPEG (baseline JPEG only supports 8 bit precision). 0xA3ERR_NBASE_SCAN One or more of the JPEG scan header parameters Ss, Se, Ahand Al is set to a value not supported by baseline JPEG (indicatingspectral selection and/or successive approximation which are notsupported in baseline JPEG). 0xA4 ERR_UNEXPECTED_DNL During JPEGoperation a DNL marker has been encountered in a scan that is not thefirst scan in a frame. 0xA5 ERR_EOS_UNEXPECTED During JPEG operation onEOS marker has been encountered in an unexpected place 0xA6ERR_RESTART_SKIP During JPEG operation a restart marker has beenencountered either in in an unexpected place or the value of the restartmarker is unexpected. If a restart marker is not found when one isexpected the Huffman event “Found serial data when Token expected” willbe generated. 0xB0 ERR_SKIP_INTRA During MPEG operation, a macro blockwith a macro blocks address increment greater than 1 has been foundwithin an intra (1) picture. This is illegal and probably indicates abitstream error. 0xB1 ERR_SKIP_DINTRA During MPEG operation, a macroblock with a macro block address increment greater than 1 has been foundwithin an DC only (D) picture. This is illegal and probably indicates abitstream error. 0xB2 ERR_BAD_MARKER During MPEG operation, a marker bitdid not have the expected value. This is probably indicates a bitstreamerror. 0xB3 ERR_D_MBTYPE During MPEG operation, within a DC only (D)picture, a macroblock was found with a macroblock type other than 1.This is illegal and probably indicates a bitstream error. 0xB4ERR_D_MBEND During MPEG operation, within a DC only (D) picture, amacroblock was found with 0 in its end of macroblock bit. This isillegal and probably indicates a bitstream error. 0xB5 ERR_SVP_BACKUPDuring MPEG operation, a slice has been encountered with a slicevertical position less than that expected. This is likely to indicate anerror in the coded data 0xB6 ERR_SVP_SKIP_ROWS During MPEG operation, aslice has been encountered with a slice vertical position greater thanthat expected. This is likely to indicate an error in the coded data0xB7 ERR_FST_MBA_BACKUP During MPEG operation, a macroblock has beenencountered with a macro block address less than that expected. This islikely to indicate an error in the coded data 0xB8 ERR_FST_MBA_SKIPDuring MPEG operation, a macroblock has been encountered with a macroblock address greater than that expected. This is likely to indicate anerror in the coded data 0xB9 ERR_PICTURE_END_UNEXPECTED During MPEGoperation, a PICTURE_END Token has been encountered in an unexpectedplace. This is likely to indicate an error in the coded data. 0xE0 ...0xEF Errors reserved for internal test programs 0xE0 ERR_TST_PROGRAMMysteriously arrived in the test program 0xE1 ERR_NO_PROGRAM If the testprogram is not compiled in 0xE2 ERR_TST_END End of Test 0xF0 ... 0xFFReserved errors 0xF0 ERR_UCODE_ADDR fell of the end of the world 0xF1ERR_NOT_IMPLEMENTED

[1368] Each standard uses a different sub-set of the defined Parsererror codes. TABLE A.14.13 Parser error codes and the differentstandards Token Name MPEG JPEG H.251 ERR_NO_ERROR ✓ ✓ ✓ERR_EXTENSION_TOKEN ✓ ✓ ERR_EXTENSION_DATA ✓ ✓ ERR_USER_TOKEN ✓ ✓ERR_USER_DATA ✓ ✓ ERR_PSPARE ✓ ERR_GSPARE ✓ ERR_PTYPE ✓ ERR_JPEG_FRAME ✓ERR_JPEG_FRAME_LAST ✓ ERR_JPEG_SCAN ✓ ERR_JPEG_SCAN_COMP ✓ERR_DNL_MARKER ✓ ERR_MPEG_SEQUENCE ✓ ERR_EXTRA_PICTURE ✓ ERR_EXTRA_SLICE✓ ERR_VBV_DELAY ✓ ERR_SHORT_TOKEN ✓ ✓ ✓ ERR_H261_PIC_END_UNEXPECTED ✓ERR_GN_BACKUP ✓ ERR_GN_SKIP_GOB ✓ ERR_NBASE_TAB ✓ ERR_QUANT_PRECISION ✓ERR_SAMPLE_PRECISION ✓ ERR_NBASE_SCAN ✓ ERR_UNEXPECTED_DNL ✓ERR_EOS_UNEXPECTED ✓ ERR_RESTART_SKIP ✓ ERR_SKIP_INTRA ✓ ERR_SKIP_DINTRA✓ ERR_BAD_MARKER ✓ ERR_D_MBTYPE ✓ ERR_D_MBEND ✓ ERR_SVP_BACKUP ✓ERR_SVP_SKIP_ROWS ✓ ERR_FST_MBA_BACKUP ✓ ERR_FST_MBA_SKIP ✓ERR_PICTURE_END_UNEXPECTED ✓ ERR_TST_PROGRAM ✓ ✓ ✓ ERR_NO_PROGRAM ✓ ✓ ✓ERR_TST_END ✓ ✓ ✓ ERR_UCODE_ADDR ✓ ✓ ✓ ERR_NOT_IMPLEMENTED ✓ ✓ ✓

[1369] A.14.6 Receiving User and Extension Data

[1370] MPEC and JPEG use similar mechanisms to embed user and extensiondata. The data is preceded by a start/marker code. The Start CodeDetector can be configured to delete this data (see A.11.3.3) if theapplication has no interest in such data.

[1371] A.14.6.1 Identifying the source of the Data

[1372] The Parser events, ERR_EXTENSION_TOKEN and ERR_USER_TOKEN,indicate the arrival of the EXTENSION_DATA or USER_DATA Token at theVideo Demux. If these Tokens have been generated by the Start CodeDetector, (see A.11.3.3) they will carry the value of the start/markercode that caused the Start Code Detector to generate the Token (seeTable A.11.4). This value can be read by reading the rom_revisionregister while servicing the Parser interrupt. The Video Demux willremain halted until 1 is written to parser_event (see A.6.3, ”Interrupts”).

[1373] A.14.6.2 Reading the Data

[1374] The EXTENSION_DATA and USER_DATA Tokens are expected to beimmediately followed by a DATA Token carrying the extension or userdata. The arrival of this DATA Token at the Video Demux will generateeither an ERR_EXTENSION_DATA or an ERR_USER_DATA Parser event. The firstbyte of the DATA Token can be read by reading the rom_revision registerwhile servicing the interrupt.

[1375] The state of the Video Demux register, continue, determinesbehavior after the event is cleared. If this register holds the value 0,then any remaining data in the DATA Token will be consumed by the VideoDemux and no events will be generated. If the continue is set to 1, anevent will be generated as each byte of extension or user data arrivesat the Video Demux. This continues until the DATA Token is exhausted orcontinue is set to 0.

[1376] Note:

[1377] 1) The first byte of the extension/user data is always presentedvia the rom_revision register regardless of the state of continue.

[1378] 2) There is no event indicating that the last byte ofextension/user data has been read.

[1379] A.14.7 Receiving Extra Information

[1380] H.261 and MPEG allow information extending the coding standard tobe embedded within pictures and groups of blocks (H.261) or slices(MPEG). The mechanism is different from that used for extension and userdata (described in Section A.14.6). No start code precedes the data and,thus, it cannot be deleted by the Start Code Detector.

[1381] During H.261 operation, the Parser events ERR_PSPARE andERR_GSPARE indicate the detection of this information. The correspondingevents during MPEG operation are ERR_EXTRA_PICTURE and ERR_EXTRA_SLICE.

[1382] When the Parser event is generated, the first byte of the extrainformation is presented through the register, rom_revision.

[1383] The state of the Video Demux register, continue, determinesbehavior after the event is cleared. If this register holds the value 0,then any remaining extra information will be consumed by the Video Demuxand no events will be generated. If the continue is set to 1, an eventwill be generated as each byte of extra information arrives at the VideoDemux. This continues until the extra information is exhausted orcontinue is set to 0.

[1384] Note:

[1385] 1) The first byte of the extension/user data is always presentedvia the rom_revision register regardless of the state of continue.

[1386] 2) There is no event indicating that the last byte ofextension/user data has been read.

[1387] A.14.7.¹ Generation of the FIELD_INFO Token

[1388] During MPEG operation, if the register field_info is set to 1,the first byte of any extra_information_picture is placed in theFIELD_INFO Token. This behavior is not covered by the standardizationactivities of MPEG. Table A.3.2 shows the definition of the FIELD_INFOToken.

[1389] If field_info is set to 1, no Parser event will be generated forthe first byte of extra_information_picture. However, events will begenerated for any subsequent bytes of extra_information_picture. Ifthere is only a single byte of extra_information_picture, no Parserevent will occur.

[1390] A.14.8 Changes at the MPEG Sequence Layer

[1391] The MPEG sequence header describes the following characteristicof the video about to be decoded:

[1392] horizontal and vertical size

[1393] pixel aspect ratio

[1394] picture rate

[1395] coded data rate

[1396] video buffer verifier buffer size

[1397] If any of these parameters change when the Spatial Decoderdecodes a sequence header, the Parser event ERR_MPEG_SEQUENCE will begenerated.

[1398] A.14.8.1 Change in Picture Size

[1399] If the picture size has changed, the user's software should readthe values in horiz_pels and vert_pels and compute new values to beloaded into the registers horiz_macroblocks and vert_macroblocks.

[1400] Section A.15 Spatial Decoding

[1401] In accordance with the present invention, the spatial decodingoccurs between the output of the Token buffer and the output of theSpatial Decoder.

[1402] There are three main units responsible for spatial decoding: theinverse modeler, the inverse quantizer and the inverse discrete cosinetransformer. At the input to this section (from the Token buffer) DATATokens contain a run and level representation of the quantizedcoefficients. At the output (of the inverse DCT) DATA Tokens contain Bx8blocks of pixel information.

[1403] A.15.1 The Inverse Modeler

[1404] DATA Tokens in the Token buffer contain information about thevalues of quantized coefficients and the number of zeros between thecoefficients that are represented. The Inverse Modeler expands theinformation about runs of zeros so that each DATA Token contains 64values. At this point, the values in the DATA Tokens are quantizedcoefficients.

[1405] The inverse modelling process is the same regardless of thecoding standard currently being used. No configuration is required.

[1406] For a better understanding of the modelling and inverse modellingfunction all requirements the reader can examine any of the picturecoding standards.

[1407] A.15.2 Inverse Quantizer

[1408] In an encoder, the quantizer divides down the output of the DCTto reduce the resolution of the DCT coefficients. In a decoder, thefunction of the inverse quantizer is to multiply up these quantized DCTcoefficients to restore them to an approximation of their originalvalues.

[1409] A.15.2.1 Overview of the Standard Quantization Schemes

[1410] There are significant differences in the quantization scheme usedby each of the different coding standards. To obtain a detailedunderstanding of the quantization schemes used by each of the standardsthe reader should study the relevant coding standards documents.

[1411] The register iq_coding_standard configures the operation of theinverse quantizer to meet the requirements of the different standards.In normal operation, this coding register is automatically loaded by theCODING_STANDARD Token. See section A.21.1 for more information aboutcoding standard configuration.

[1412] The main difference between the quantization schemes is thesource of the numbers by which the quantized coefficients aremultiplied. These are outlined below. There are also detail differencesin the arithmetic operations required (rounding etc.), which are notdescribed here.

[1413] A.15.2.1.1 H.261 lQ Overview

[1414] In H.261, a single “scale factor” is used to scale thecoefficients. The encoder can change this scale factor periodically toregulate the data rate produced. Slightly different rules apply to the“DC” coefficient in intra coded blocks.

[1415] A.15.2.1.2 JPEG lQ Overview

[1416] Baseline JPEG allows for a picture that contains up to 4different color components in each scan. For each of these 4 colorcomponents, a 64 entry quantization table can be specified. Each entryin these tables is used as the “scale” factor for one of the 64quantized coefficients.

[1417] The values for the JPEG quantization tables are contained in thecoded JPEG data and will be loaded automatically into the quantizationtables.

[1418] A.15.2.1.3 MPEG lo Overview

[1419] MPEG uses both H.261 and JPEG quantization techniques. Like JPEG,4 quantization tables, each with 64 entries, can be used. However, useof the tables is quite different.

[1420] Two “types” of data are considered: intra and non-intra. Adifferent table is used for each data type. Two “default” tables aredefined by MPEG. One is for use with intra data and the other withnon-intra data (see Table A.15.2 and Table A.15.3). These default tablesmust be written into the quantization table memory of the SpatialDecoder before MPEG decoding is possible.

[1421] MPEG also allows two “down loaded” quantization tables. One isfor use with intra data and the other with non-intra data. The valuesfor these tables are contained in the MPEG data stream and will beloaded into the quantization table memory automatically.

[1422] The value output from the tables is modified by a scale factor.

[1423] A.15.2.2 Inverse Quantizer Registers TABLE A.15.1 Inversequantizer registers Register name Size/Dir. Reset State Descriptioniq_access 1 0 This access bit stops the operation of the inversequantiser so that its rw various registers can be accessed reliably. SeeA.6.4.1 iq_coding_standard 2 0 This register configures the codingstandard used by the inverse rw quantiser. The register can be loadeddirectly or by a CODING_STANDARD Token. See A.21 1 iq_keyhole_address 8x Keyhole access to the which holds the 4 quantiser tables. See A.5 4 0rw for more information about accessing registers through aiq_keyhole_data 8 x keyhole. rw

[1424] In the present invention, the iq_access register must be setbefore the quantization table memory can be accessed. The quantizationtable memory will return the value zero if an attempt is made to read itwhile iq_access is set to 0.

[1425] 3 A.15.2.3 Configuring the Inverse Quantizer

[1426] In normal operation, there is no need to configure the inversequantizer's coding standard as this will be automatically configured bythe CODING_STANDARD Token.

[1427] For H.261 operation, the quantizer tables are not used. Nospecial configuration is required. For JPEG operation, the tablesrequired by the inverse quantizer should be automatically loaded withinformation extracted from the coded data.

[1428] MPEG operation requires that the default quantization tables areloaded. This should be done while iq access is set to 1. The values inTable A.15.2 should be written into locations 0x00 to 0x3F of theinverse quantizer's extended address space (accessible through thekeyhole registers iq_keyhole_address and iq_keyhole_data). Similarly,the values in Table A.15.3 should be written into locations 0x40 to 0x7Fof the inverse quantizer's extended address space. TABLE A.15.2 DefaultMPEG table for intra coded blocks i^(a) W_(i,0) ^(b) 0 8 1 16 2 16 3 194 16 5 19 6 22 7 22 8 22 9 22 10 22 11 22 12 26 13 24 14 26 15 27 16 2717 27 18 25 19 26 20 26 21 26 22 27 23 27 24 27 25 29 26 29 27 29 28 3429 34 30 34 31 29 32 29 33 29 34 27 35 27 36 29 37 29 38 32 39 32 40 3441 34 42 37 43 38 44 37 45 35 46 35 47 34 48 35 49 38 50 38 51 40 52 4053 40 54 48 55 48 58 46 57 46 58 56 59 56 60 58 61 69 62 69 63 83

[1429] TABLE A.15.3 Default MPEG table for non-intra coded blocks iW_(i,1) 0 16 1 16 2 16 3 16 4 16 5 16 6 16 7 16 8 16 9 16 10 16 11 16 1216 13 16 14 16 15 16 16 16 17 16 18 16 19 16 20 16 21 16 22 16 23 16 2416 25 16 26 16 27 16 28 16 29 16 30 16 31 16 32 16 33 16 34 16 35 16 3616 37 16 38 16 39 16 40 16 41 16 42 16 43 16 44 16 45 16 46 16 47 16 4816 49 16 50 16 51 16 52 16 53 16 54 16 55 16 56 16 57 16 58 16 59 16 6016 61 16 62 16 63 16

[1430] A.15.2.4 Configuring Tables from Tokens

[1431] As an alternative to configuring the inverse quantizer tables viathe MPI, they can be initialized by Tokens. These Tokens can be suppliedvia either the coded data port or the MPI.

[1432] The QUANT_TABLE Token is described in Table A.3.2. It has a twobit field tt which specifies which of the 4 (0 to 3) table locations isdefined by the Token. For MPEG operation, the default definitions oftables 0 and 1 need to be loaded.

[1433] A.15.2.5 Quantization Table Values

[1434] For both JPEG and MPEG, the quantization table entries are 8 bitnumbers. The values 255 to 1 are legal. The value 0 is illegal.

[1435] A.15.2.6 Number Ordering of Quantization Tables

[1436] The quantization table values are used in “zig-zag” scan order(see the coding standards). The tables should be viewed as a onedimensional array of 64 values (rather than a 8×8 array). The tableentries at lower addresses correspond to the lower frequency DCTcoefficients.

[1437] When quantization table values are carried by a QUANT_TABLEToken, the first value after the Token header is the table entry for the“DC” coefficient.

[1438] A.15.7 Inverse Quantizer Test Registers TABLE A.15.4 Inversequantizer test registers Register Name Size/Dir. Reset State Descriptioniq_quant_scale 5 This register holds the current value of thequantisation scale factor. rw It is loaded by the QUANT_SCALE Token.This is not used during JPEG operation iq_component 2 This registerholds the two bit component ID taken from the most rw recent DATA tokenhead. This value is involved in the selection of the quantiser table.The register will also hold the table ID after a QUANT_TABLE Tokenarrives to load the table. iq_prediction_mode 2 This holds the two LSBsof the most recent PREDICTION_MODE rw Token. iq_jpeg_indirection 8 Thisregister relates the two bit component ID number of a DATA rw Token tothe table number of the quantisation table that should be used. Bits 1:0specify the table number that will be sued with component 0 Bits 3:2specify the table number that will be sued with component 1 Bits 5:4specify the table number that will be sued with component 2 Bits 7:6specify the table number that will be sued with component 3. Thisregister is loaded by JPEG_TABLE_SELECT Tokens. iq_mpeg_indirection 2 0This two bit register records whether to use default or down loaded rwquantisation tables with the intra and non-intra data. A 0 in the bitposition indicates that the default table should be used. A.1 indicatesthat a down loaded table should be used. Bit 0 refers to intra data. Bit1 refers to non-intra data. This register is normally loaded by theToken MPEG_TABLE_SELECT.

[1439] A.15.3 Inverse Discrete Cosine Transform

[1440] The inverse discrete transform processor of the present inventionmeets the requirements set out in CCITT recommendation H.261, the IEEEspecification P1180 and complies with the requirements described incurrent draft revision of MPEG.

[1441] The inverse discrete cosine transform process is the sameregardless of which coding standard is used. No, configuration by theuser is required.

[1442] There are two events associated with the inverse discretetransform processor. TABLE A.15.5 Inverse DCT event registers Registername Size/Dir. Reset State Description idct_too_few_event 1 0 TheInverse DCT requires that all DATA Tokens contain exactly 64 rw values.If less than 64 values are found then the too-few event will beidct_too_few_mask 1 0 generated. If the mask register is set to 1 thenan interrupt can be rw generated and the Inverse DCT will halt. Thisevent should only occur following an error in the coded data.idct_too_many_event 1 0 The Inverse DCT requires that all DATA Tokenscontain exactly 64 rw values. If more than 64 values are found then thetoo-many event will be idct_too_many_mask 1 0 generated. If the maskregister is set to 1 then an interrupt can be rw generated and theInverse DCT will halt. This event should only occur following an errorin the coded data.

[1443] For a better understanding of the DCT and inverse DCT functionthe reader can examine any of the picture coding standards.

[1444] Section A.16 Connecting to the Output of Spatial Decoder

[1445] The output of the Spatial Decoder is a standard Token Port with 9bit wide data words. See Section A.4 for more information about theelectrical behavior of the interface.

[1446] The Tokens present at the output will depend on the codingstandard employed. By way of example, this section of the disclosurelooks at the output of the Spatial Decoder when configured for JPEGoperation. This section also describes the Token sequence observed atthe output of the Temporal Decoder during JPEG operation as the TemporalDecoder doesn't modify the Token sequence that results from decodingJPEG.

[1447] However, MPEG and H.261 both require the use of the TemporalDecoder. See section A.19 for information about connecting to the outputof the Temporal Decoder when configured for MPEG and H.261 operation.

[1448] Furthermore, this section identifies which of the Tokens areavailable at the output of the Spatial Decoder and which are most usefulwhen designing circuits to display that output. Other Tokens will bepresent, but are not needed to display the output and, therefore, arenot discussed here.

[1449] This section concentrates on showing:

[1450] How the start and end of sequences can be identified.

[1451] How the start and end of pictures can be identified.

[1452] How to identify when to display the picture.

[1453] How to identify where in the display the picture data should beplaced.

[1454] A.16.1 Structure of JPBG Pictures

[1455] This section provides an overview of some features of the JPEGsyntax. Please refer to the coding standard for full details.

[1456] JPEG provides a variety of mechanisms for encoding individualpictures. JPEG makes no attempt to describe how a collection of picturescould be encoded together to provide a mechanism for encoding video.

[1457] The Spatial Decoder, in accordance with the present invention,supports JPEG's baseline sequential mode of operation. There are threemain levels in the syntax: Image, Frame and Scan. A sequential imageonly contains a single frame. A frame can contain between 1 and 256different image (color) components. These image components can begrouped, in a variety of ways, into scans. Each scan can contain between1 and 4 image components (see FIG. 81 “Overview of JPEG baselinesequential structure”).

[1458] If a scan contains a single image component, it isnon-interleaved, if it contains more than one image component, it is aninterleaved scan. A frame can contain a mixture of interleaved andnon-interleaved scans. The number of scans that a frame can contain isdetermined by the 256 limit on the number of image components that aframe can contain.

[1459] Within an interleaved scan, data is organized into minimum codingunits (MCUs) which are analogous to the macroblock used in MPEG andH.261. These MCUs are raster ordered within a picture. In anon-interleaved scan, the MCU is a single 8×8 block. Again, these areraster organized.

[1460] The Spatial Decoder can readily decode JPEG data containing 1 to4 different color components. Files describing greater numbers ofcomponents can also be decoded. However, some reconfiguration betweenscans may be required to accommodate the next set of components to bedecoded.

[1461] A. 16.2 Token Sequence

[1462] The JPEG markers codes are converted to an analogous MPEG namedToken by the Start Code Detector (see Table A.11.4, see FIG. 82“Tokenized JPEG picture”).

[1463] Section A. 17 Temporal Decoder

[1464] 30 MH, operation

[1465] Provides temporal decoding for MPEG & H.261 video decoders

[1466] H.261 CIF and QCIF formats

[1467] MPEG video resolutions up to 704×480, 30 Hz, 4:2:0

[1468] Flexible chroma sampling formats

[1469] Can re-order the MPEG picture sequence

[1470] Glue-less DRAM interface

[1471] Single +5V supply

[1472] 208 pin PQFP package

[1473] Max. power dissipation 2.5 W

[1474] Uses standard page mode DRAM

[1475] The Temporal Decoder is a companion chip to the Spatial Decoder.It provides the temporal decoding required by H.261 and MPEG.

[1476] The Temporal Decoder implements all the prediction formingfeatures required by MPEG and H.261. With a single 4 Mb DRAM (e.g., 512k×8) the Temporal Decoder can decode CIF and QCIF H.261 video. With 8 Mbof DRAM (e.g., two 256 k×16) the 704×480, 30 Hz, 4:2:0 MPEG video can bedecoded.

[1477] The Temporal Decoder is not required for Intra coding schemes(such as JPEG). If included in a multi-standard decoder, the TemporalDecoder will pass decoded JPEG pictures through to its output.

[1478] Note: The above values are merely illustrative, by way of exampleand not necessarily by way of limitation, of one embodiment of thepresent invention. It will be appreciated that other values and rangesmay also be used without departing from the invention.

[1479] A.17.1 Temporal Decoder Signals TABLE A.17.1 Temporal DecoderSignals Signal Name I/O Pin Number Description in_data[8:0] I 173, 172,171, 169, 168, 167, 166, 164, 163 Input Port. This is a standard twowire in_extn I 174 interface normally connected to the in_valid I 162Output Port of the Spatial Decoder. in_accept O 161 See sections A.4 andA.181 {overscore (enable)}[1:0] I 126, 127 Micro Processor Interface(MPI) r{overscore (w)} I 125 See A.6.1. on page 69 addr[7:0] I 137, 136,135, 133, 132, 131, 130, 128 data[7:0] O 152, 151, 149, 147, 145, 143,141, 140 {overscore (irq)} O 154 DRAM_data[31:0] I/O 15, 17, 19, 20, 22,25, 27, 30, 31, 33, 35, DRAM Interface. 38, 39, 42, 44, 47, 49, 57, 59,61, 63, 66 See section A.5.2 68, 70, 72, 74, 76, 79, 81, 83, 84, 85DRAM_addr[10:0] O 184, 186, 188, 189, 192, 193, 195, 197, 199, 200, 203{overscore (RAS)} O 11 {overscore (CAS)}[3:0] O 2, 4, 6, 8 {overscore(WE)} O 12 {overscore (OE)} O 204 DRAM_enable I 112 out_data[7:0] O 89,90, 92, 93, 94, 95, 97, 98 Output Port. This is a standard two out_extnO 87 wire interface. out_valid O 99 See sections A.4 and A.19 out_acceptI 100 tck I 115 JTAG port. tdi I 116 See section A.8 tdo O 120 tms I 117{overscore (trst)} I 121 decoder_clock I 177 The main decoder clock. SeeTable A.7.2 {overscore (reset)} I 160 Reset.

[1480] TABLE A.17.2 Temporal Decoder Test signals Signal Name I/O PinNum. Description tph0ish I 122 If override = 1 then tph0ish and tph1ishare inputs for the on-chip tph1ish I 123 two phase clock. override I 110For normal operation set override = 0. tph0ish and tph1ish are ignored(so connect to GND or V_(DD)). chiptest I 111 Set chiptest = 0 fornormal operation. tlooo I 114 Connect to GND or V_(DD) during normaloperation. ramtest I 109 If ramtest = 1 test of the on-chip RAMs isenabled. Set ramtest = 0 for normal operation. pllselect I 178 Ifpllselect = 0 the on-chip phase locked loops are disabled. Set pllslect= 1 for normal operation. tl I 180 Two clocks required by the DRAMinterface during test operation tq I 179 Connect to GND or V_(DD) duringnormal operation. pdout O 207 These two pins are connections for an pdinI 206 external filter for the phase lock loop.

[1481] TABLE A.17.3 Temporal Decoder Pin Assignments Signal Name Pin nc208 test pin 207 test pin 206 GND 205 OE 204 DRAM_addr[0] 203 VDD 202 nc201 DRAM_addr[1] 200 DRAM_addr[2] 199 GND 198 DRAM_addr[3] 197 nc 196DRAM_addr[4] 195 VDD 194 DRAM_addr[5] 193 DRAM_addr[6] 192 nc 191 GND190 DRAM_addr[7] 189 DRAM_addr[8] 188 VDD 187 DRAM_addr[9] 186 nc 185DRAM_addr[10] 184 GND 183 nc 182 VDD 181 test pin 180 test pin 179 testpin 178 decoder_clock 177 nc 176 GND 175 in_extn 174 in_data[8] 173in_data[7] 172 in_data[6] 171 VDD 170 in_data[5] 169 in_data[4] 168in_data[3] 167 in_data[2] 166 GND 165 in_data[1] 164 in_data[0] 163in_valid 162 in_accept 161 reset 160 VDD 159 nc 158 nc 157 nc 156 nc 155irq 154 nc 153 data[7] 152 data [6] 151 nc 150 data[5] 149 nc 148data[4] 147 GND 146 data[3] 145 nc 144 data[2] 143 nc 142 data[1] 141data[0] 140 nc 139 VDD 138 addr[7] 137 addr[6] 136 addr[5] 135 GND 134addr[4] 133 addr[3] 132 addr[2] 131 addr[1] 130 VDD 129 addr[0] 128{overscore (enable)}[0] 127 {overscore (enable)}[1] 126 rw 125 GND 124test pin 123 test pin 122 trst 121 tdo 120 nc 119 VDD 118 tms 117 tdf116 tck 115 test pin 114 GND 113 DRAM_enable 112 test pin 111 test pin110 test pin 109 nc 108 nc 107 nc 106 nc 105 nc 104 nc 103 nc 102 VDO101 out_accept 100 out_valid 99 out_data[0] 98 out_data[1] 97 GND 96out_data[2] 95 out_data[3] 94 out_data[4] 93 out_data[5] 92 VDO 91out_data[6] 90 out_data[7] 89 nc 88 out_extn 87 GND 86 DRAM_data[0] 85DRAM_data[1] 84 DRAM_data[2] 83 VDD 82 DRAM_data[3] 81 nc 80DRAM_data[4] 79 GND 78 nc 77 DRAM_data[5] 76 nc 75 DRAM_data[5] 74 VDD73 DRAM_data[7] 72 nc 71 DRAM_data[8] 70 GND 69 DRAM_data[9] 68 nc 67DRAM_data[10] 66 VDD 65 nc 64 DRAM_data[11] 63 nc 62 DRAM_data[12] 61GND 60 DRAM_data[13] 59 nc 58 DRAM_data[14] 57 VDD 56 nc 55 nc 54 nc 53nc 52 nc 51 nc 50 DRAM_data[15] 49 nc 48 DRAM_data[16] 47 nc 46 GND 45DRAM_data[17] 44 nc 43 DRAM_data[18] 42 VDO 41 nc 40 DRAM_data[19] 39DRAM_data[20] 38 nc 37 GND 36 DRAM_data[21] 35 nc 34 DRAM_data[22] 33VDD 32 DRAM_data[23] 31 DRAM_data[24] 30 nc 29 GND 28 DRAM_data[25] 27nc 26 DRAM_data[25] 25 nc 24 VDD 23 DRAM_data[27] 22 nc 21 DRAM_data[28]20 DRAM_data[29] 19 GND 18 DRAM_data[30] 17 nc 16 DRAM_data[31] 15 VDD14 nc 13 {overscore (WE)} 12 {overscore (RAS)} 11 nc 10 GND 9 {overscore(CAS)}[0] 8 nc 7 {overscore (CAS)}[1] 6 VDD 5 {overscore (CAS)}[2] 4 nc3 {overscore (CAS)}[3] 2 nc 1

[1482] A.17.1.1 “nc” No Connect Pins

[1483] The pins labelled nc in Table A.17.3 are not currently used inthe present invention and are reserved for future products. These pinsshould be left unconnected. They should not be connected to VDD, GND,each other or any other signal.

[1484] A.17.1.2 V_(DD) and GND Pins

[1485] As will be appreciated all the V_(DD) and GND pins provided mustbe connected to the appropriate power supply. The device will notoperate correctly unless all the V_(DD) and GND pins are correctly used.

[1486] A.17.1.3 Test Pin Connections for Normal Operation

[1487] Nine pins on the Temporal Decoder are reserved for internal testuse. TABLE A.17.4 Default test pin connections Pin number ConnectionConnect to GND for normal operation Connect to V_(DD) for normaloperation Leave Open Circut for normal operation

[1488] A.17.4 JTAG Pins for Normal Operation

[1489] See Section A.8.1. TABLE A.17.5 Overview of Temporal Decodermemory map Addr. (hex) Register Name See table 0x00 ... 0x01 Interruptservice area A.17.6 0x02 ... 0x07 Not used 0x08 Chip access A.17.7 0x09... 0x0F Not used 0x10 Picture sequencing A.17.3 0x11 ... 0x1F Not used0x20 ... 0x2E DRAM interface configuration registers A.17.9 0x2F ...0x3F Not used 0x40 ... 0x53 Buffer configuration A.17.3 0x54 ... 0x5FNot used 0x60 ... 0xFF Test registers A.17.11

[1490] TABLE A.17.6 Interrupt service area registers Addr. Bit (hex)num. Register Name Page references 0x00 7 chip_event 6.2 not used 1chip_stopped_event 0 count_error_event 0x01 7 chip_mask 6.2 not used 1chip_stopped_mask 0 count_error_mask

[1491] TABLE A.17.7 Chip access register Addr. Bit (hex) num. RegisterName Page references 0x08 7:1 not used 0 chip_access

[1492] TABLE A.17.8 Picture sequencing Addr. Bit (hex) num. RegisterName Page references 0x10 7:1 not used 0 MPEG_reordering

[1493] TABLE A.17.9 DRAM interface configuration registers Addr. Bit(hex) num. Register Name Page references 0x20 7:5 not used 4:0page_start_length[4:0] 0x21 7:4 not used 3:0 read_cycle_length[3:0] 0x227:4 not used 3:0 write_cycle_length[3:0] 0x23 7:4 not used 3:0refresh_cycle_length[3:0] 0x24 7:4 not used 3:0 CAS_falling[3:0] 0x257:4 not used 3:0 RAS_falling[3:0] 0x26 7:1 not used 0Interface_timing_access 0x27 7:0 not used 0x28 7:6 RAS_strength[2:0] 5:3OEWE_strength[3:0] 2:0 DRAM_data_strength[3:0] 0x29 7 not used 6:4DRAM_addr_strength[3:0] 3:1 CAS_strength[3:0] 0 RAS_strength[3] 0x28 7not used 6:4 DRAM_addr_strength[3:0] 3:1 CAS_strength[3:0] 0RAS_strength[3] 0x29 7:6 RAS_strength[2:0] 5:3 OEWE_strength[3:0] 2:0DRAM_data_strength[3:0] 0x2A 7:0 refresh_interval 0x2B 7:0 not used 0x2C7:6 not used 5 DRAM_enable 4 no_refresh 3:2 row_address_bits[1:0] 1:0DRAM_data_width[1:0] 0x2D 7:0 not used 0x2E 7:0 Test registers

[1494] TABLE A.17.10 Buffer configuration registers Addr. Bit (hex) num.Register Name Page references 0x40 7:0 not used 0x41 7:2 1:0picture_buffer_0[17:0] 0x42 7:0 0x43 7:0 0x44 7:0 not used 0x45 7:2 1:0picture_buffer_1[17:0] 0x46 7:0 0x47 7:0 0x48 7:0 not used 0x49 7:1 0component_offset_0[16:0] 0x4A 7:0 0x4B 7:0 0x4C 7:0 not used 0x4D 7:1 0component_offset_1[16:0] 0x4E 7:0 0x4F 7:0 0x50 7:0 not used 0x51 7:1 0component_offset_2[16:0] 0x52 7:0 0x53 7:0

[1495] TABLE A.17.11 Test registers Addr. Bit (hex) num. Register NamePage references 0x2E 7 . . . 4 PLL resistors 3 . . . 0 0x60 7 . . . 6not used 5 . . . 4 coding_standard[1:0] 3 . . . 2 picture_type[1:0] 1H261_filt 0 H261_s_f 0x61 7 . . . 6 component_id 5 . . . 4prediction_mode 3 . . . 0 max_sampling 0x62 7 . . . 0 samp_h 0x63 7 . .. 0 samp_v 0x64 7 . . . 0 back_h 0x65 7 . . . 0 0x66 7 . . . 0 back_v0x67 7 . . . 0 0x68 7 . . . 0 forw_h 0x69 7 . . . 0 0x6A 7 . . . 0forw_v 0x6B 7 . . . 0 0x6C 7 . . . 0 width_in_mb 0x6D 7 . . . 0

[1496] SECTION A.18 Temporal Decoder Operation

[1497] A.18.1 Data Input

[1498] The input data port of the Temporal Decoder is a standard TokenPort with 9 bit wide data words. In most applications, this will beconnected directly to the output Token Port of the Spatial Decoder. SeeSection A.4 for more information about the electrical behavior of thisinterface.

[1499] A.18.2 Automatic Configuration

[1500] Parameters relating to the coded video's picture format areautomatically loaded into registers within the Temporal Decoder byTokens generated by the Spatial Decoder. TABLE A.18.1 Configuration ofTemporal Decoder via Tokens Token Configuration performedCODING_STANDARD The coding standard of the Temporal Decoder isautomatically configured by the CODING_STANDARD Token. This is generatedby the Spatial Decoder each time a new sequence is started. See FIG. 58DEFINE_SAMPLING The horizontal and vertical chroma sampling informationfor each of the color components is automatically configured byDEFINE_SAMPLING Tokens. HORIZONTAL_MBS The horizontal width of picturesin macro blocks is automatically configured by HORIZONTAL_MBS Token.

[1501] A.18.3 Manual Configuration

[1502] The user must configure (via the microprocessor interface)application dependent factors.

[1503] A18.3.1 When to Configure

[1504] The Temporal Decoder should only be configured when no dataprocessing is taking place. This is the default state after reset isremoved. The Temporal Decoder can be stopped to allow re-configurationby writing 1 to the chip_access register. After configuration iscomplete, 0 should be written to chip_access.

[1505] See Section A.5.3 for details of when to configure the DRAMinterface.

[1506] A.18.3.2 DRAM Interface

[1507] The DRAM interface timing must be configured before it ispossible to decode predictively coded video (e.g., H.261 or MPEG). SeeSection A.5, “DRAM Interface”. TABLE A.18.2 Temporal Decoder registersRegister Name Size/Dir. Reset State Description chip_access  1 1 Writing1 to chip_access requests that the Temporal Decoder halt operation tochip_stopped_event  1 0 allow re-configuration. The Temporal Decoderwill continue operating normally until it reaches the end of the currentvideo sequence. After reset is removed chip_access=1 i.e. the TemporalDecoder is halted. chip_stopped_mask  1 0 When the chip stops a chipstopped event will occur. If chip_stopped_mask = 1 an interrupt will begenerated. count_error_event  1 0 The Temporal Decoder has an adder thatadds predictions to error data. If there rw is a difference between thenumber of error data bytes and the number of prediction data bytes thena count error event is generated. If count_error_mask = 1 an interruptwill be generated and prediction forming will stop. count_error_mask  1This event should only arise following a hardware error. rwpicture_buffer_0 18 x These specify the base addresses for the picturebuffers. picture_buffer_1 18 x component_offset_0 17 x These specify theoffset from the picture buffer pointer at which each of thecomponent_offset_1 17 x colour components is stored. Data with componentID = n is stored starting at rw the position indicated bycomponent_offset_n. See A.3.5.1, “Component component_offset_2 17 xIdentification number”. MPEG_recording  1 0 Setting this register to 1makes the Temporal Decoder change the picture order rw from thenon-causal MPEG picture sequence to the correct display order by the.See A.18.3.5. This register should is ignored during JPEG and H.261operation.

[1508] A.18.3.3 Numbers in Picture Buffer Registers

[1509] The picture buffer pointers (18 bit) and the component offset (17bit) registers specify a block (8×8 bytes) address, not a byte address.

[1510] A.18.3.4 Picture Buffer Allocation

[1511] To decode predictively coded video (either H.261 or MPEG) theTemporal Decoder must manage two picture buffers. See Section A.18.4 andA.18.4.4 for more information about how these buffers are used.

[1512] The user must ensure that there is sufficient memory above eachof the picture buffer pointers (picture_buffer_(—)0 andpicture_buffer_(—)1) to store a single picture of the required videoformat (without overlapping with the other picture buffer). Normally,one of the picture buffer pointers will be set to 0 (i.e., the bottom ofmemory) and the other will be set to point to the middle of the memoryspace.

[1513] A.18.3.4.1 Normal Configuration for MPEG or H.261

[1514] H.261 and MPEG both use a 4:1:1 ratio between the different colorcomponents (i.e., there are 4 times as many luminance pels as there arepels in either of the chrominance components).

[1515] As documented in Section A.3.5.1, “Component Identificationnumber”, component 0 will be the luminance component and components 1and 2 will be chrominance.

[1516] An example configuration of the component offset registers is toset component_offset_(—)0 to 0 so that component 0 starts at the picturebuffer pointer. Similarly, component_offset_(—)1 could be set to 4/6 ofthe picture buffer size and component offset 2 could be set to 5/6 ofthe picture buffer size.

[1517] A.18.3.5 Picture Sequence Re-ordering

[1518] MPEG uses three different picture types: Intra (I), Predicted (P)and Bidirectionally interpolated (B). B pictures are based onpredictions from two pictures: one from the future and one from thepast. The picture order is modified at the encoder so that I and Ppicture can be decoded from the coded date before they are required todecode B pictures.

[1519] The picture sequence must be corrected before these pictures canbe displayed. The Temporal Decoder can provide this picture re-ordering(by setting register MPEG_reordering=1). Alternatively, the user maywish to implement the picture re-ordering as part of his displayinterface function. Configuring the Temporal Decoder to provide picturere-ordering may reduce the video resolution that can be decoded, seeSection A.18.5.

[1520] A.18.4 Prediction Forming

[1521] The prediction forming requirements of H.261 decoding and MPEGdecoding are quite different. The CODING_STANDARD Token automaticallyconfigures the Temporal Decoder to accommodate the predictionrequirements of the different standards.

[1522] A.18.4.1 JPEG Operation

[1523] When configured for JPEG operation no predictions are performedsince JPEG requires no temporal decoding.

[1524] A.18.4.2 E.261 Operation

[1525] In H.261, predictions are only from the picture just decoded.Motion vectors are only specified to integer pixel accuracy. The encodercan specify that a low pass filter be applied to the result of anyprediction.

[1526] As each picture is decoded, it is written in to a picture bufferin the off-chip DRAM so that it can be used in decoding the nextpicture. Decoded pictures appear at the output of the Temporal Decoderas they are written into the off-chip DRAM.

[1527] For full details of prediction, and the arithmetic operationsinvolved, the reader is directed to the H.261 standard. The TemporalDecoder of the present invention is fully compliant with therequirements of H.261.

[1528] A.18.4.3 MPEG Operation (without Re-ordering)

[1529] The operation of the Temporal Decoder changes for each of thethree different MPEG picture types (I, P and B).

[1530] “I” pictures require no further decoding by the Temporal Decoder,but must be stored in a picture buffer (frame store) for later use indecoding P and B pictures.

[1531] Decoding P pictures requires forming predictions from apreviously decoded P or I picture. The decoded P picture is stored in apicture buffer for use in decoding P and B pictures. MPEG allows motionvectors specified to half pixel accuracy. On-chip filters provideinterpolation to support this half pixel accuracy.

[1532] B pictures can require predictions from both of the picturebuffers. As with P pictures, half pixel motion vector resolutionaccuracy requires on chip interpolation of the picture information. Bpictures are not stored in the off-chip buffers. They are merelytransient.

[1533] All pictures appear at the output port of the Temporal Decoder asthey are decoded. So, the picture sequence will be the same as that inthe coded MPEG data (see the upper part of FIG. 85).

[1534] For full details of prediction, and the arithmetic operationsinvolved, the reader is directed to the proposed MPEG standard draft.These requirements are met by the Temporal Decoder of the presentinvention.

[1535] A.18.4.4 MPEG Operation (with Re-ordering)

[1536] When configured for MPEG operation with picture re-ordering(MPEG_reordering=1), the prediction forming operations are as describedabove in Section A.18.4.3. However, additional data transfers areperformed to re-order the picture sequence.

[1537] B picture decoding is as described in section A.18.4.3. However,I and P pictures are not output as they are decoded. Instead, they arewritten into the off-chip buffers (as previously described) and are readout only when a subsequent I or P picture arrives for decoding.

[1538] A.18.4.4.1 Decoder Start-up Characteristics

[1539] The output of the first I picture is delayed until the subsequentP (or I) picture starts to decode. This should be taken intoconsideration when estimating the start-up characteristics of a videodecoder.

[1540] A.18.4.4.2 Decoder Shut-down Characteristics

[1541] The Temporal Decoder relies on subsequent P or I pictures toflush previous pictures out of its off-chip buffers (frame stores). Thishas consequences at the end of video sequences and when starting newvideo sequences. The Spatial Decoder provides facilities to create a“fake” I/P picture at the end of a video sequence to flush out the lastP (or I) picture. However, this “fake” picture will be flushed out whena subsequent video sequence starts.

[1542] The Spatial Decoder provides the option to suppress this “fake”picture. This may be useful where it is known that a new video sequencewill be supplied to the decoder immediately after an old sequence isfinished. The first picture in this new sequence will flush out the lastpicture of the previous sequence.

[1543] A.18.5 Video Resolution

[1544] The video resolution that the Temporal Decoder can support whendecoding MPEG is limited by the memory bandwidth of its DRAM interface.For MPEG, two cases need to be considered: with and without MPEG picturere-ordering.

[1545] Sections A.18.5.2 and A.18.5.3 discuss the worst caserequirements required by the current draft of the MPEG specification.Subsets of MPEG can be envisioned that have lower memory bandwidthrequirements. For example, using only integer resolution motion vectorsor, alternatively, not using B pictures, significantly reduce the memorybandwidth requirements. Such subsets are not analyzed here.

[1546] A18.5.1 Characteristics of DRAM Interface

[1547] The number of cycles taken to transfer data across the DRAMinterface depends on a number of factors:

[1548] The timing configuration of the DRAM interface to suite the DRAMemployed

[1549] The data bus width (8, 16 or 32 bits)

[1550] The type of data transfer:

[1551] 8×8 block read or write

[1552] for prediction to half pixel accuracy

[1553] for prediction to integer pixel accuracy

[1554] See section A.5, “DRAM Interface”, for more information about thedetail configuration of the DRAM interface.

[1555] Table A.18.3 shows how many DRAM interface “cycles” are requiredfor each type of data transfer. TABLE A.18.3 Data transfer times forTemporal Decoder Data bus form prediction width read or write 8x8 formprediction (integer pixel (bits) block (half pixel accuracy) accuracy) 8 1 page address + 64 4 page address + 81 4 page address + transferstransfers 64 transfers 16 1 page address + 32 4 page address + 45 4 pageaddress + transfers transfers 40 transfers 32 1 page address + 16 4 pageaddress + 27 4 page address + transfers transfers 24 transfers

[1556] Table A.18.4 takes the figures in Table A.18.3 and evaluates themfor a “typical” DRAM. In this example, a 27 MHz clock is assumed. Itwill be appreciated that while 27 MHz is used here, it is not intendedas a limitation. The access start takes 11 ticks (102 ns) and the datatransfer takes 6 ticks (56 ns).

[1557] A.18.5.2 MPEG Resolution without Re-ordering

[1558] The peak memory bandwidth load occurs when decoding B pictures.In a “worst case” scenario, the B frame may be formed from predictionsfrom both the picture buffers with all predictions being to half pixelaccuracy. TABLE A.18.4 Illustration with “typical” DRAM Data bus formprediction width read or write 8x form prediction (integer pixel (bits)8 block (half pixel accuracy) accuracy) 8 3657 ns 4907 ns 3963 ns 161880 ns 2907 ns 2185 ns 32  991 ns 1907 ns 1741 ns

[1559] Using the example figures from Table A.18.4, it can be seen thatit will take the DRAM interface 3815 ns to read the data required fortwo accurate half pixel accurate predictions (via a 32 bit wideinterface). The resolution that the Temporal Decoder can support isdetermined by the number of these predictions that can be performedwithin one picture time. In this example, the Temporal Decoder canprocess 8737×8 blocks in a single 33 ms picture period (e.g., for 30 Hzvideo).

[1560] If the required video format is 704×480, then each picturecontains 7920 8×8 blocks (taking into consideration the 4:2:0 chromasampling). It can be seen that this video format consumes approx. 91% ofthe available DRAM interface bandwidth (before any other factors such asDRAM refresh are taken into consideration). Accordingly, the TemporalDecoder can support this video format.

[1561] A.18.5.3 MPEG Resolution with Re-ordering

[1562] When MPEG picture re-ordering is employed the worst case scenariois encountered while P pictures are being decoded. During this time,there are 3 loads on the DRAM interface:

[1563] form predictions

[1564] write back the result

[1565] read out the previous P or I picture

[1566] Using the example figures from Table A.18.3, we can find the timeit takes for each of these tasks when a 32 bit wide interface isavailable. Forming the prediction takes 1907 ns/n while the read and thewrite each take 991 ns, a total of 3889 ns. This permits the TemporalDecoder to process 8485 8×8 blocks in a 33 ms period.

[1567] Hence, processing 704×480 video will use approximately 93% of theavailable memory bandwidth (ignoring refresh).

[1568] A.18.5.4 H.261

[1569] H.261 only supports two picture formats CIF (352×288) and QCIF(172×144) at picture rates up to 30 Hz. A CIF picture contains 2376 8×8blocks. The only memory operations required are the writing of 8×8blocks and the forming of predictions with integer accuracy motionvectors.

[1570] Using the example figures from Table A.18.4 for an 8 bit widememory interface, it can be seen that writing each block will take 3657ns while forming the prediction for one block will take 3963 ns/n, atotal of 7620 ns per block. Therefore, the processing time for a singleCIF picture is about 18 ms, comfortably less than the 33 ms required tosupport 30 Hz video.

[1571] A.18.5.5 JPEG

[1572] The resolution of JPEG “video” that can be supported will bedetermined by the capabilities of the Spatial Decoder of the inventionor the display interface. The Temporal Decoder does not affect JPEGresolution.

[1573] A.18.6 Events and Errors

[1574] A.18.6.1 Chip Stopped

[1575] In the present invention, writing 1 to chip_access requests thatthe Temporal Decoder halt operation to allow re-configuration. Oncereceived, the Temporal Decoder will continue operating normally until itreaches the end of the current video sequence. Thereafter, the TemporalDecoder is halted.

[1576] When the chip halts, a chip stopped event will occur. Ifchip_stopped_mask=1, an interrupt will be generated.

[1577] A.18.6.2 Count Error

[1578] The Temporal Decoder, of the present invention, contains an adderthat adds predictions to error data. If there is a difference betweenthe number of error data bytes and the number of prediction data bytes,then a count error event is generated.

[1579] If count_error_mask=1 an interrupt will be generated and formingprediction will stop.

[1580] Writing 1 to count_error_event clears the event and allows theTemporal Decoder to proceed. The DATA Token that caused the error willthen proceed. However, the DATA Token that caused the error will not beof the correct length (64 bytes). This is likely to cause furtherproblems. Thus, a count error should only arise if a significanthardware error has occurred.

[1581] SECTION A.19 Connecting to the Output of the Temporal Decoder

[1582] The output of the Temporal Decoder is a standard Token Port with8 bit wide data words. See Section A.4 for more information about theelectrical behavior of the interface.

[1583] The Tokens present at the output of the Temporal Decoder willdepend on the coding standard employed and, in the case of MPEG, whetherthe pictures are being re-ordered. This section identifies which of theTokens are available at the output of the Temporal decoder and which arethe most useful when designing circuits to display that output. OtherTokens will be present, but are not needed to display the output and,therefore they are not discussed here.

[1584] This section concentrates on showing:

[1585] How the start and end of sequences can be identified.

[1586] How the start and end of pictures can be identified.

[1587] How to identify when to display the picture.

[1588] How to identify where in the display the picture data should beplaced.

[1589] A.19.1 JPEG Output

[1590] The Token sequence output by the Temporal Decoder when decodingJPEG data is identical to that seen at the output of Spatial Decoder.Recall, JPEG does not require processing by the Temporal Decoder.However, the Temporal Decoder tests intra data Tokens for negativevalues (resulting from the finite arithmetic precision of the IDCT inthe Spatial Decoder) and replaces them with zero.

[1591] See Section A.16 for further discussion of the output sequenceobserved during JPEG operation.

[1592] A.19.2 H.261 Output

[1593] A.19.2.1 Start and End of Sessions

[1594] H.261 doesn't signal the start and end of the video stream withinthe video data. Nevertheless, this is implied by the application. Forexample, the sequence starts when the telecommunication connection ismade and ends when the line is dropped. Thus, the highest layer in thevideo syntax is the “picture layer”.

[1595] The Start Code Detector of the Spatial Decoder in accordance withthe invention, allows SEQUENCE_START and CODING_STANDARD Tokens to beinserted automatically before the first PICTURE_START. See sectionsA.11.7.3 and A.11.7.4.

[1596] At the end of an H.261 session (e.g., when the line is dropped)the user should insert a FLUSH Token after the end of the coded data.This has a number of effects (see Appendix A.31.1:

[1597] It ensures that PICTURE_END is generated to signal the end of thelast picture.

[1598] It ensures that the end of the coded data is pushed through thedecoder.

[1599] A.19.2.2 Acquiring Pictures

[1600] Each picture is composed of a hierarchy of elements referred toas layers in the syntax. The sequence of Tokens at the output of theTemporal Decoder when decoding H.261 reflects this structure.

[1601] A.19.2.1 Picture Layer

[1602] Each picture is preceded by a PICTURE_START Token and each isimmediately followed by a PICTURE_END Token. H.261 doesn't naturallycontain a picture end. This Token is inserted automatically by the StartCode Detector of the Spatial Decoder.

[1603] After the PICTURE_START Token, there will be TEMPORAL_REFERENCEand PICTURE_TYPE Tokens. The TEMPORAL_REFERENCE Token carries a 10 bitnumber (of which only the 5 LSBs are used in H.261) that indicates whenthe picture should be displayed. This should be studied by any displaysystem as H.261 encoders can omit pictures from the sequence (to achievelower data rates). Omission of pictures can be detected by the temporalreference incrementing by more than one between successive pictures.

[1604] Next, the PICTURE_TYPE Token carries information about thepicture format. A display system may study this information to detect ifCIF or QCIF pictures are being decoded. However, information about thepicture format is also available by studying registers within theHuffman decoder.

[1605] <Xref to Huffman decoder section>

[1606] A.19.2.2.2 Group of Blocks Layer

[1607] Each H.261 picture is composed of a number of “groups of blocks”.Each of these is preceded by a SLICE_START Token (derived from the H.261group number and group start code). This Token carries an 8 bit valuethat indicates where in the display the group of blocks should beplaced. This provides an opportunity for the decoder to resynchronizeafter data errors. Moreover, it provides the encoder with a mechanism toskip blocks if there are areas of a picture that do not requireadditional information in order to describe them. By the timeSLICE_START reaches the output of the Temporal Decoder, this informationis effectively redundant as the Spatial Decoder and Temporal Decoderhave already used the information to ensure that each picture containsthe correct number of blocks and that they are in the correct positions.Hence, it should be possible to compute where to position a block ofdata output by the Temporal Decoder just by counting the number ofblocks that have been output since the start of the picture.

[1608] The number carried by SLICE_START is one less than the H.261group of blocks number (see the H.261 standard for more information).FIG. 94 shows the positioning of H.261 groups of blocks within CIF andQCIF pictures. NOTE: in the present invention, the block numbering shownis the same as that carried by SLICE_START. This is different from theH.261 convention for numbering these groups.

[1609] Between the SLICE_START (which indicates the start of each groupof blocks) and the first macroblock there may be other Tokens. These canbe ignored as they are not required to display the picture data.

A.19.2.2.3 Macroblock Layer

[1610] The sequence of macroblocks within each group of blocks isdefined by H.261. There is no special Token information describing theposition of each macroblock. The user should count through themacroblock sequence to determine where to display each piece ofinformation.

[1611]FIG. 96 shows the sequence in which macroblocks are placed in eachgroup of blocks.

[1612] Each macroblock contains 6 DATA Tokens. The sequence of DATATokens in each group of 6 is defined by the H.261 macroblock structure.Each DATA Token should contain exactly 64 data bytes for an 8×8 area ofpixels of a single color component. The color component is carried in a2 bit number in the DATA Token (see section A.3.5.1). However, thesequence of the color components in H.261 is defined.

[1613] Each group of DATA Tokens is preceded by a number of Tokenscommunicating information about motion vectors, quantizer scale factorsand so forth. These Tokens are not required to allow the pictures to bedisplayed and, thus, can be ignored.

[1614] Each DATA Token contains 64 data bytes for an 8×8 of a singlecolor component. These are in a raster order.

[1615] A.19.3 MPEG Output

[1616] MPEG has more layers in its syntax. These embody concepts such asa video sequence and the group of pictures.

[1617] A.19.3.1 MPEG Sequence Layer

[1618] A sequence can have multiple entry points (sequence starts) butshould have only a single exit point (sequence end). When an MPEGsequence header code is decoded, the Spatial Decoder generates aCODING_STANDARD Token followed by a SEQUENCE_START Token.

[1619] After the SEQUENCE_START, there will be a number of Tokens ofsequence header information that describe the video format and the like.See the draft MPEG standard for the information that is signalled in thesequence header and Table A.3.2 for information about how this data isconverted into Tokens. This information describing the video format isalso available in registers in the Huffman decoder.

[1620] This sequence header information may occur several times withinan MPEG sequence, if that sequence has several entry points. A.19.3.2Group of pictures layer An MPEG group of pictures provides a differenttype of “entry” point to that provided at a sequence start. The sequenceheader provides information about the picture/video format. Accordingly,if the decoder has no knowledge of the video format used in a sequence,it must start at a sequence start. However, once the video format isconfigured into the decoder, it should be possible to start decoding atany group of pictures.

[1621] MPEG doesn't limit the number of pictures in a group. However, inmany applications a group will correspond to about 0.5 seconds, as thisprovides a reasonable granularity of random access.

[1622] The start of a group of pictures is indicated by a GROUP_STARTToken. The header information provided after GROUP_START includes twouseful Tokens: TIME_CODE and BROKEN_CLOSED.

[1623] TIME_CODE carries a subset of the SMPTE time code information.This may be useful in synchronizing the video decoder to other signals.BROKEN_CLOSED carries the MPEG closed_gap and broken_link bits. SeeSection A.19.3.8 for more on the implications of random access anddecoding edited video sequences.

[1624] A.19.3.3 Picture Layer

[1625] The start of a new picture is indicated by the PICTURE_STARTToken. After this Token, there will be TEMPORAL_REFERENCE andPICTURE_TYPE Tokens. The temporary reference information may be usefulif the Temporal Decoder is not configured to provide picturere-ordering. The picture type information may be useful if a displaysystem wants to specially process B pictures at the start of an open GOP(see Section A. 19.3.8).

[1626] Each picture is composed of a number of slices.

[1627] A.19.3.4 Slice Layer

[1628] Section A.19.2.2.2 discusses the group of blocks used in H.261.The slice in MPEG serves a similar function. However, the slicestructure is not fixed by the standard. The 8 bit value carried by theSLICE_START Token is one less than the “slice vertical position”communicated by MPEG. See the draft MPEG standard for a description ofthe slice layer.

[1629] By the time SLICE_START reaches the output of the TemporalDecoder, this information is effectively redundant since the SpatialDecoder and Temporal Decoder have already used the information to ensurethat each picture contains the correct number of blocks in the correctpositions. Hence, it should be possible to compute where to position ablock of data output by the Temporal Decoder just by counting the numberof blocks that have been output since the start of the picture.

[1630] See section A.19.3.7 for discussion of the effects of using MPEGpicture re-ordering.

[1631] A.19.3.5 Macroblock Layer

[1632] Each macroblock contains 6 blocks. These appear at the output ofthe Temporal Decoder in raster order (as specified by the draft MPEGspecification).

[1633] A.19.3.6 Block Layer

[1634] Each macroblock contains 6 DATA Tokens. The sequence of DATATokens in each group of 6 is defined by the draft MPEG specification(this is the same as the H.261 macroblock structure). Each DATA tokenshould contain exactly 64 data bytes for an 8×8 area of pixels of asingle color component. The color component is carried in a 2 bit numberin the DATA Token (see A.3.5.1). However, the sequence of the colorcomponents in MPEG is defined.

[1635] Each group of DATA Tokens is preceded by a number of Tokenscommunicating information about motion vectors, quantizer scale factors,and so forth. These Tokens are not required to allow the pictures to bedisplayed and, therefore, they can be ignored.

[1636] A.19.3.7 Effect of MPEG Picture Re-ordering

[1637] As described in A.18.3.5, the Temporal Decoder can be configuredto provide MPEG picture re-ordering (MPEG_reordering=1). The output of Pand I pictures is delayed until the next P/I picture in the data streamstarts to be decoded by the Temporal Decoder. At the output of theTemporal Decoder the DATA Tokens of the newly decoded P/I picture arereplaced with DATA Tokens from the older P/I picture.

[1638] When re_ordering P/I pictures, the PICTURE_START,TEMPORAL_REFERENCE and PICTURE_TYPE Tokens of the picture are storedtemporarily on-chip as the picture is written into the off-chip picturebuffers. When the picture is read out for display, these stored Tokensare retrieved. Accordingly, re-ordered P/I pictures have the correctvalues for PICTURE_START, TEMPORAL_REFERENCE and PICTURE_TYPE.

[1639] All other tokens below the picture layer are not re-ordered. Asthe re-ordered P/I picture is read-out for display it picks up the lowerlevel non-DATA tokens of the picture that has just been decoded. Hence,these sub-picture layer Tokens should be ignored.

[1640] A.19.3.8 Random Access and Edited Sequences

[1641] The Spatial Decoder provides facilities to help correct videodecoding of edited MPEG video data and after a random access into MPEGvideo data.

[1642] A.19.3.8.1 Open GOPs

[1643] A group of pictures (GOP) can start with B pictures that arepredicted from a P picture in a previous GOP. This is called an “openGOP”. FIG. 107 illustrates this. Pictures 17 and 18 are B pictures atthe start of the second GOP. If the GOP is “open”, then the encoder mayhave encoded these two pictures using predictions from the P picture 16and also the I picture 19. Alternatively, the encoder could haverestricted itself to using predictions from only the I picture 19. Inthis case, the second GOP is a “closed GOP”.

[1644] If a decoder starts decoding the video at the first GOP, it willhave no problems when it encounters the second GOP even if that GOP isopen since it will have already decoded the P picture 16. However, ifthe decoder makes a random access and starts decoding at the second GOPit cannot decode B17 and B18 if they depend on P16 (i.e., if the GOP isopen).

[1645] If the Spatial Decoder of the present invention encounters anopen GOP as the first GOP following a reset or it receives a FLUSHToken, it will assume that a random access to an open GOP has occurred.In this case, the Huffman decoder will consume the data for the Bpictures in the normal way. However, it will output B pictures predictedwith (0,0) motion vectors off the I picture. The result will be thatpictures B17 and B18 (in the example above) will be identical to I19.

[1646] This behavior ensures correct maintenance of the MPEG VBV rules.Also, it ensures that B pictures exist in the output at positions withinthe output stream expected by the other data channels. For example, theMPEG system layer provides presentation time information relating audiodata to video data. The video presentation time stamps refer to thefirst displayed picture in a GOP, i.e., the picture with temporalreference 0. In the example above, the first displayed picture after arandom access to the second GOP is B17.

[1647] The BROKEN_CLOSED Token carries the MPEG closed_gop bit. Hence,at the output of the Temporal Decoder it is possible to determine if theB pictures output are genuine or “substitutes” have been introduced bythe Spatial Decoder. Some applications may wish to take special measureswhen these “substitute” pictures are present.

[1648] A.19.3.8.2 Edited Video

[1649] If an application edits an MPEG video sequence, it may break therelationship between two GOPs. If the GOP after the edit is an open GOPit will no longer be possible to correctly decode the B pictures at thebeginning of the GOP. The application editing the MPEG data can set thebroken_link bit in the GOP after the edit to indicate to the decoderthat it will not be able to decode these B pictures.

[1650] If the Spatial Decoder encounters a GOP with a broken link, theHuffman decoder will decode the data for the B pictures in the normalway. However, it will output B pictures predicted with (0,0) motionvectors off the I picture. The result will be that pictures B17 and B18(in the example above) will be identical to I19.

[1651] The BROKEN_CLOSED Token carries the MPEG broken_link bit. Hence,at the output of the Temporal Decoder it is possible to determine if theB pictures output are genuine or “substitutes” that have been introducedby the Spatial Decoder. Some applications may wish to take specialmeasures when these “substitute” pictures are present.

[1652] SECTION A.20 Late Write DRAM Interface

[1653] The interface is configurable in two ways:

[1654] The detail timing of the interface can be configured toaccommodate a variety of different DRAM types

[1655] The “width” of the DRAM interface can be configured to provide acost/performance trade-off TABLE A.20.1 DRAM interface signals Input/Signal Name Output Description DRAM_data[31:0] I/O The 32 bit wide DRAMdata bus. Optionally this bus can be configured to be 16 or 8 bits wide.DRAM_addr[10:0] O The 22 bit wide DRAM interface address is timemultiplexed over this 11 bit wide bus. {overscore (RAS)} O The DRAM RowAddress Strobe signal {overscore (CAS)}[3:0] O The DRAM Column AddressStrobe signal. One signal is provided per byte of the interface's databus. All the {overscore (CAS)} signals are driven simultaneously.{overscore (WE)} O The DRAM Write Enable signal {overscore (OE)} O TheDRAM Output Enable signal DRAM_enable I This input signal, when low,makes all the output signals on the interface go high impedance andstops activity on the DRAM interface

[1656] TABLE A.20.2 DRAM Interface configuration registers size/ ResetRegister name dir. State Description Modify_DRAM_timing 1 bit 0 Thisfunction enable register allows access to the DRAM interface rw timingconfiguration registers. The configuration registers should not bemodified while this register holds the values zero. Writing a one tothis register requests access to modify the configuration registers.After a zero has been written to this register the DRAM interface willstart to use the new values in the timing configuration registers.page_start_length 5 bit 0.00 Specifies the length of the access start inticks. The minimum value rw that can be used is 4 (meaning 4 ticks). 0selects the maximum length of 32 ticks. read_cycle_length 4 bit 0.00Specifies the length of the fast page read cycle in ticks. The minimumrw value that can be used is 4 (meaning 4 ticks). 0 selects the maximumlength of 16 ticks. write_cycle_length 4 bit 0.00 Specifies the lengthof the fast page late write cycle in ticks. The rw minimum value thatcan be used is 4 (meaning 4 ticks). 0 selects the maximum length of 16ticks. refresh_cycle_length 4 bit 0.00 Specifies the length of therefresh cycle in ticks. The minimum value rw that can be used is 4(meaning 4 ticks). 0 selects the maximum length of 16 ticks. RAS_falling4 bit 0.00 Specifies the number of ticks after the start of the accessstart that rw {overscore (RAS)} falls. The minimum value that can beused is 4 (meaning 4 ticks). 0 selects the maximum length of 16 ticks.CAS_falling 4 bit 8 Specifies the number of ticks after the start of aread cycle, write cycle rw or access start that {overscore (CAS)} falls.The minimum value that can be used is 1 (meaning 1 tick). 0 selects themaximum length of 16 ticks. DRAM_data_width 2 bit 0.00 Specifies thenumber of bits used on the DRAM interface data bus rw DRAM_data[31:0].See A.20.4. row_address_bits 2 bit 0.00 Specifies the number of bitsused for the row address portion of the rw DRAM interface address bus.See A.20.5. DRAM_enable 1 bit 1 Writing the value 0 in to this registerforces the DRAM interface into a rw high impedance state. 0 will be readfrom this register if either the DRAM_enable signal is low or 0 has beenwritten to the register. refresh_interval no_refresh 8 bit 0.00 Thisvalue specifies the interval between refresh cycles in periods of rw 16decoder_clock cycles. Values in the range 1..255 can be configured. Thevalue 0 is automatically loaded after reset and forces the DRAMinterface to continuously execute refresh cycles until a valid refreshinterval is configured. It is recommended that refresh_interval shouldbe configured only once after each reset. CAS_strength 1 bit 0.00Writing the value 1 to this register prevents execution of any refreshrw cycles RAS_strength 3 bit 6 These three bit registers configure theoutput drive strength of DRAM addr_strength rw interface signals. Thisallows the interface to be configured for various DRAM_data_strengthdifferent loads. OEWE_strength See A.20.8.

[1657] A.20.1 Interface Timing (Ticks)

[1658] In the present invention, the DRAM interface timing is derivedfrom a clock which is running at four times the input clock rate of thedevice (decoderclock). This clock is generated by an on-chip PLL.

[1659] For brevity, periods of this high speed clock are referred to asticks.

[1660] A.20.2 Interface Operation

[1661] The interface uses of the DRAM fast page mode. Three differenttypes of access are supported:

[1662] Read

[1663] Write

[1664] Refresh

[1665] Each read or write access transfers a burst of between 1 and 64bytes at a single DRAM page address. Read and write transfers are notmixed within a single access. Each successive access is treated as arandom access to a new DRAM page.

[1666] A.20.3 Access Structure

[1667] Each access is composed of two parts:

[1668] Access start

[1669] Data transfer

[1670] Each access starts with an access start and is followed by one ormore data transfer cycles. There is a read, write and refresh variant ofboth the access start and the data transfer cycle.

[1671] At the end of the last data transfer in an access the interfaceenters it's default state and remains in this state until a new accessis ready to start. If a new access is ready to start when the lastaccess finishes, then the new access will start immediately.

[1672] A.20.3.1 Access Start

[1673] The access start provides the page address for the read or writetransfers and establishes some initial signal conditions. There arethree different access starts:

[1674] Start of read

[1675] Start of write

[1676] Start of refresh

[1677] In each case the timing of {overscore (RAS)} and the row addressis controlled by the registers RAS_falling and page_start_length. Thestate of {overscore (OE)} and DRAM_data[31:0] is held from the end ofthe previous data transfer until RAS falls. The three different accessstart types are only different in how they drive {overscore (OE)} andDRAM_data[31:0) when {overscore (RAS)} falls. See FIG. 109. TABLE A.20.3Access start parameters Num. Characteristic Min. Max. Unit Notes 38{overscore (RAS)} precharge period set by register RAS_falling 4 16 tck39 Access start duration set by register page_start_length 4 32 40{overscore (CAS)} precharge length set by register CAS_falling. 1 16^(a) 41 Fast page read cycle length set by the register 4 16read_cycle_length. 42 Fast page write cycle length set by the register 416 write_cycle_length. 43 {overscore (WE)} falls one bck after{overscore (CAS.)} 44 Refresh cycle length set by the registerrefresh_cycle. 4 16

[1678] A.20.3.2. Data Transfer

[1679] There are three different types of data transfer cycle:

[1680] Fast page read cycle

[1681] Fast page late write cycle

[1682] Refresh cycle

[1683] A start of refresh is only followed by a single refresh cycle. Astart of read (or write) can be followed by one or more fast page read(or write) cycles.

[1684] At the start of the read cycle {overscore (CAS)} is driven highand the new column address is driven.

[1685] A late write cycle is used. {overscore (WE)} is driven low onetick after {overscore (CAS)}. The output data is driven one tick afterthe address.

[1686] As a {overscore (CAS)} before {overscore (RAS)} refresh cycle isinitiated by the start of refresh cycle, there is no interface signalactivity during a refresh cycle. The purpose of the refresh cycle is tomeet the minimum {overscore (RAS)} low period required by the DRAM.

[1687] A.20.3.3 Interface Default State

[1688] The interface signals enter a default state at the end of anaccess:

[1689] {overscore (RAS)}, {overscore (CAS)} and {overscore (WE)} high

[1690] data and OE remain in their previous state

[1691] addr remains stable

[1692] A.20.4 Data Bus Width

[1693] The two bit register DRAM_data_width allows the width of the DRAMinterfaces data path to be configured. This allows the DRAM cost to beminimized when working with small picture formats. TABLE A.20.4Configuring DRAM_data_width DRAM_data_width  0^(a)  8 bit wide data buson DRAM_data[31:24]^(b). 1 16 bit wide data bus on DRAM_data[31:16]^(b)2 32 bit wide data bus on DRAM_data[31:0]

[1694] A.20.5 Address Bits

[1695] On-chip, a 24 bit address is generated. How this address is usedto form the row and column addresses depends on the width of the databus and the number of bits selected for the row address. Someconfigurations do not permit all the internal address bits to be used(and) therefore, produce “hidden bits).

[1696] The row address is extracted from the middle portion of theaddress. This maximizes the rate at which the DRAM is naturallyrefreshed.

[1697] A.20.5.1 Low Order Column Address Bits

[1698] The least significant 4 to 6 bits of the column address are usedto provide addresses for fast page mode transfers of up to 64 bytes. Thenumber of address bits required to control these transfers will dependon the width of the data bus (see A.20.4).

[1699] A.20.5.2 Row Address Bits

[1700] The number of bits taken from the middle section of the 24 bitinternal address to provide the row address is configured by theregister row_address_bits. TABLE A.20.5 Configuring row_address_bitsrow_address_bits Width of row address 0  9 bits 1 10 bits 2 11 bits

[1701] The width of row address used will depend on the type of DRAMused and whether the MSBs of the row address are decoded off-chip toaccess multiple banks of DRAM.

[1702] NOTE: The row address is extracted from the middle of theinternal address. If some bits of the row address are decoded to selectbanks of DRAM, then all possible values of these “bank select bits” mustselect a bank of DRAM. Otherwise, holes will be left in the addressspace. TABLE A.20.6 Selecting a value for row_address_bitsrow_address_bits row address bits bank select DRAM depth 0DRAM_addr[8:0]  256k 1 DRAM_addr[8:0] DRAM_addr[9]  256k DRAM_addr[9:0] 512k DRAM_addr[9:0] 1024k 2 DRAM_addr[8:0] DRAM_addr[10:9]  256kDRAM_addr[9:0] DRAM_addr[10]  512k DRAM_addr[9:0] DRAM_addr[10] 1024kDRAM_addr[10:0] 2048k DRAM_addr[10:0] 4096k

[1703] A.20.6 DRAM Interface Enable

[1704] There are two ways to make all the output signals on the DRAMinterface become high impedance. The DRAM_enable register and theDRAM_enable signal. Both the register and the signal must be at a logic1 for the DRAM interface to operate. If either is low, then theinterface is taken to high impedance and data transfers through theinterface are halted.

[1705] The ability to take the DRAM interface to high impedance isprovided in order to allow other devices to test or to use the DRAMcontrolled by the Spatial Decoder (or the Temporal Decoder) when theSpatial Decoder (or the Temporal Decoder) is not in use. It is notintended to allow other devices to share the memory during normaloperation.

[1706] A.20.7 Refresh

[1707] Unless disabled by writing to the register, no refresh, the DRAMinterface will automatically refresh the DRAM using a {overscore (CAS)}before {overscore (RAS)} refresh cycle at an interval determined by theregister refresh_interval.

[1708] The value in refresh_interval specifies the interval betweenrefresh cycles in periods of 16 decoder_clock cycles. Values in therange 1 to 255 can be configured. The value 0 is automatically loadedafter reset and forces the DRAM interface to continuously executerefresh cycles (once enabled) until a valid refresh interval isconfigured. It is recommended that refresh_interval should be configuredonly once after each reset.

[1709] A.20.8 Signal Strengths

[1710] The drive strength of the outputs of the DRAM interface can beconfigured by the user using the 3 bit registers, CAS_strength,RAS_strength, addr_strength, DRAM_datastrength, OEWE_strength. The MSBof this 3 bit value selects either a fast or slow edge rate. The twoless significant bits configure the output for different loadcapacitances.

[1711] The default strength after reset is 6, configuring the outputs totake approximately 10 ns to drive signal between GND and V_(DD) ifloaded with 12_(F)F. TABLE A.20.7 Output strength configurationsstrength value Drive characteristics 0 Approx. 4 ns/V into 6 pf load 1Approx. 4 ns/V into 12 pf load 2 Approx. 4 ns/V into 24 pf load 3Approx. 4 ns/V into 48 pf load 4 Approx. 2 ns/V into 6 pf load 5 Approx.2 ns/V into 12 pf load  6^(a) Approx. 2 ns/V into 24 pf load 7 Approx. 2ns/V into 48 pf load

[1712] When an output is configured approximately for the load it isdriving, it will meet the AC electrical characteristics specified inTables A.20.11 to Table A.20.12. When appropriately configured eachoutput is approximately matched to it's load and, therefore, minimalovershoot will occur after a signal transition.

[1713] A.20.9 After Reset

[1714] After reset, the DRAM interface configuration registers are allreset to their default values. most significant of these defaultconfigurations are:

[1715] The DRAM interface is disabled and allowed to go high impedance.

[1716] The refresh interval is configured to the special value 0 whichmeans execute refresh cycle continuously after the interface isre-enabled.

[1717] The DRAM interface is set to it's slowest configuration.

[1718] Most DRAMs require a “pause” of between 100μs and 500 μs afterpoker is first applied, followed by a number of refresh cycles beforenormal operation is possible.

[1719] Immediately after reset, the DRAM interface is inactive untilboth the DRAM_enable signal and the DRAM_enable register are set. Whenthese have been set, the DRAM interface will execute refresh cycles(approximately every 400 ns, depending upon the clock frequency used)until the DRAM interface is configured.

[1720] The user is responsible for ensuring that the DRAM's “pause”after power_up and for allowing sufficient time after enabling the DRAMinterface to ensure that the required number of refresh cycles haveoccurred before data transfers are attempted.

[1721] While reset is asserted, the DRAM interface is unable to refreshthe DRAM. However, the reset time required by the decoder chips issufficiently short so that is should be possible to reset them and tothen re-enable the DRAM interface before the DRAM contents decay. Thismay be required during debugging. TABLE A.20.8 Maximum Ratings^(a)Symbol Parameter Min. Max. Units V_(OD) Supply voltage relative to −0.56.5 V GND V_(IN) Input voltage on any pin GND − 0.5 V_(OD) + 0.5 V T_(A)Operating temperature −40 +85 ° C. T_(S) Storage temperature −55 +150 °C.

[1722] TABLE A.20.9 DC Operating conditions Symbol Parameter Min. Max.Units V_(OD) Supply voltage relative to 4.75 5.25 V GND GND Ground 0 0 VV_(IH) Input logic ‘1’ voltage 2.0 V_(OD) −0.5 V V_(IL) Input logic ‘0’voltage GND −0.5 0.8 V T_(A) Operating temperature 0 70 ° C.^(a)

[1723] TABLE A.20.10 DC Electrical characteristics Symbol Parameter Min.Max. Units V_(OL) Output logic ‘0’ voltage 0.4 V^(a) V_(OH) Output logic‘1’ voltage 2.8 V I_(O) Output current ±100 μA^(b) I_(OZ) Output offstate leakage current ±20 μA I_(LZ) Input leakage current ±10 μA I_(DO)RMS power supply current 500 mA C_(IN) Input capacitance 5 pF C_(OUT)Output/IO capacitance 5 pF

[1724] A.20.10.1 AC Characteristics TABLE A.20.11 Differences fromnominal values for a strobe Num. Parameter Min. Max. Unit Note^(a) 45Cycle time e.g. tPC −2 +2 ns 46 Cycle time e.g. tRC −2 +2 ns 47 Highpulse e.g. tRP, tCP, tCPN −5 +2 ns 48 Low pulse e.g. tRAS, tCAS, tCAC,−11 +2 ns tWP, tRASP, tRASC 49 Cycle time e.g. tACP/tCPA −8 +2 ns

[1725] TABLE A.20.12 Differences from nominal values between two strobesNum. Parameter Min. Max. Unit Note^(a) 50 Strobe to strobe delay e.g.tRCD, −3 +3 ns 51 tCSR Low hold time e.g. tRSH, −13 +3 ns tCSH, tRWL,tCWL tRAC, tOAC/OE, tCHR 52 Strobe to strobe precharge e.g. tCRP, −9 +3ns tRCS, tRCH, tRRH, tRPC {overscore (CAS)} precharge pulse between any−5 +2 ns two {overscore (CAS)} signals on wide DRAMs e.g. tCP, orbetween {overscore (RAS)} rising and {overscore (CAS)} falling e.g. tRPC

[1726] TABLE A.20.12 Differences from nominal values between two strobesNum. Parameter Min. Max. Unit Note^(a) 53 Precharge before disable e.g.tRHCP/ −12 +3 ns CPRH

[1727] SECTION B.1 Start Code Detector

[1728] B.1.1 Overview

[1729] As previously shown in FIG. 11, the Start Code Detector (SCD) isthe first block on the Spatial Decoder. Its primary purpose is to detectMPEG, JPEG and H.261 start codes in the input data stream and to replacethem with relevant Tokens. It also allows user access to the input datastream via the microprocessor interface, and performs preliminaryformatting and “tidying up” of the token data stream. Recall, the SCDcan receive either raw byte data or data already assembled in Tokenformat.

[1730] Typically, start codes are 24, 16 and 8 bits wide for MPEG,H.261, and JPEG, respectively. The Start Code Detector takes theincoming data in bytes, either from the Microprocessor Interface (upi)or a token/byte port and shifts it through three shift registers. Thefirst register is an 8 bit parallel in serial out, the second registeris of programmable length (16 or 24 bits) and is where the start codesare detected, and the third register is 15 bits wide and is used toreformat the data into 15 bit tokens. There are also two “tag” ShiftRegisters (SR) running parallel with the second and third SRs. Thesecontain tags to indicate whether or not the associated bit in the dataSR is good. Incoming bytes that are not part of a DATA Token and areunrecognized by the SCD, are allowed to bypass the shift registers andare output when all three shift registers are flushed (empty) and thecontents output successfully. Recognized non-data tokens are used toconfigure the SCD, spring traps, or set flags. They also bypass theshift registers and are output unchanged.

[1731] B.1.2 Major Blocks

[1732] The hardware for the Start Code Detector consists of 10 statemachines.

[1733] B.1.2.1 Input Circuit (scdipc.sch.iplm.M)

[1734] The input circuit has three modes of operation: token, byte andmicroprocessor interface. These modes allow data to be input either as araw byte stream (but still using the two-wire interface), as a tokenstream, or by the user via the upi. In all cases, the input circuit willalways output the correct DATA Tokens by generating DATA Token headerswhere appropriate. Transitions to and from upi mode are synchronized tothe system clocks and the upi may be forced to wait until a safe pointin the data stream before gaining access. The Byte mode pin determineswhether the input circuit is in token or byte mode. Furthermore,initially informing the system as to which standard is being decoded (soa CODING STANDARD Token can be generated) can be done in any of thethree modes.

[1735] B.1.2.2 Token Decoder (scdipnew.sch, scdipnem.M)

[1736] This block decodes the incoming tokens and issues commands to theother blocks. TABLE B.1.1 Recognized input tokens Command Input Tokenissued Comments NULL WAIT NULLs are removed DATA NORMAL Load next byteinto first SR CODING_STD BYPASS Flush shift registers, perform padding,output and switch to bypass mode. Load CODING_STANDARD register. FLUSHBYPASS Flush SRs with padding, output and switch to bypass mode. ELSEBYPASS Flush SRs with padding, output and (unrecognised token) switch tobypass mode. #This principle is applied throughout the presentation sothat a change in the coding standard can flow through the whole chipprior to the new stream.

[1737] B.1.2.3 JPEG (scdjpeg.sch scdjpegm.M)

[1738] Start codes (Markers) in JPEG are sufficiently different thatJPEG has a state machine all to itself. In the present invention, thisblock handles all the JPEG marker detection, length counting/checking,and removal of data. Detected JPEG markers are flagged as start codes(with v_not_t-see later text) and the command from scdipnew isoverridden and. forced to bypass. The operation is best described incode. switch (state) { case (LOOKING): if (input == 0xff) { state =GETVALUE; /*Found a marker*/ remove; /*Marker gets removed*/ } elsestate = LOOKING; break; case (GETVALUE); if (input == 0xff) { state =GETVALUE; /*Overlapping markers*/ remove; } else if (input = 0x00) {state = LOOKING;/*Wasn't a marker*/ insert(0xff); /*Put the 0xff back*/} else { command = BYPASS; /*override command*/ if(lc) /* Does themarker have a length count*/ state = GETLC0; else state = LOOKING;break; case (GETLC0); loadlc0; /*Load the top length count byte*/ state= GETLC1; remove; break; case (GETLC1) loadlc1; remove; state = DECLC;break; case (DECLC); lent = lent − 2 state = CHECKLC; break; case(CHECKLC): if (lent == 0) state = LOOKING;/*No more to do*/ else if(lent <0) state = LOOKING;/*generate Illegal_Length_Error*/ else state =COUNT; break; case (COUNT); decrement length count until 1 if (lc <= 1)state = LOOKING; }

[1739] B.1.2.4 Input Shifter (scinshft.sch, scinshm.M)

[1740] The basic operation of this block is quite simple. This blocktakes a byte of data from the input circuit, loads the shift registerand shifts it out. However, it also obeys the commands from the inputdecoder and handles the transitions to and from bypass mode (flushingthe other SRs): On receiving a BYPASS command, the associated byte isnot loaded into the shift register. Instead “rubbish” (tag=1) is shiftedout to force any data held in the other shift registers to the output.The block then waits for a “flushed” signal indicating that this“rubbish” has appeared at the token reconstructor. The input byte isthen passed directly to the token reconstructor.

[1741] B.1.2.5 Start Code Detector (scdetect.sch, scdetm.M)

[1742] This block includes two shift registers which are programmable to16 or 24 bits, start code detection logic and “valid contents” detectionlogic. MPEG start codes require the full 24 bits, whereas H.261 requiresonly 16.

[1743] In the present invention, the first SR is for data and the secondcarries tags which indicate whether the bits in the data SR arevalid—there are no gaps or stalls (in the two-wire interface sense) inthe SRs, but the bits they contain can be invalid (rubbish) whilst theyare being flushed. On detection of a start code, the tag shift registerbits are set in order to invalidate the contents of the detector SR.

[1744] A start code cannot be detected unless the SR contents are allvalid. Non byte-aligned start codes are detected and may be flagged.Moreover, when a start code is detected, it cannot be definitely flaggeduntil an overlapping start code has been checked for. To accomplish thisfunction, the “value” of the detected start code (the byte following it)is shifted right through scinshift, scdetect and into scoshift. Havingarrived at scoshift without the detection of another start code, it isoverlapping start codes have been eliminated and it is flagged as avalid start code.

[1745] B.1.2.6 Output Shifter (scoshift.sch, scoshm.M)

[1746] The basic operation of the output shifter is to take serial data(and tags) from scdetect, pack it into 15 bit words and output them.Other functions are:

[1747] B.1.2.6.1 Data Padding

[1748] The output consists of 15 bit words, but the input may consist ofan arbitrary number of bits. In order to flush, therefore, we need toadd bits to make the last word up to 15 bits. These extra bits arecalled padding and must be recognized and removed by the Huffman block.Padding is defined to be:

[1749] After the last data bit, a “zero” is inserted followed bysufficient “ones” to make up a 15 bit word.

[1750] The data word containing the padding is output with a lowextension bit to indicate that it is the end of a data token.

[1751] B.1.2.6.2 Generation of “Flushed”

[1752] In accordance with the present invention, the generation of“flushed” operation involves detecting when all SRs are flushed andsignalling this to the input shifter. When the “rubbish” inserted by theinput shifter reaches the end of the output shifter, and the outputshifter has completed its padding, a “flushed” signal is generated. This“flushed” signal must pass through the token reconstructor before it issafe for the input shifter to enter bypass mode.

[1753] B.1.2.6.3 Flagging Valid Start Codes

[1754] If scdetect indicates that it has found a start code, padding isperformed and the current data is output. The start code value (the nextbyte) is shifted through the detector to eliminate overlapping startcodes. If the “value” arrives at the output shifter without anotherstart code being detected, it was not overlapped and the value is passedout with a flag v_not_t (ValueNotToken) to indicate that it is a startcode value. If, however, another start code is detected (by scdetect)whilst the output shifter is waiting for the value, anoverlapping_start_error is generated. In this case, the first value isdiscarded and the system then waits for the second value. This value canalso be overlapped, thus causing the same procedure to be repeated untila non-overlapped start code is found.

[1755] B.1.2.6.4 Tidying up After a Start Code

[1756] Having detected and output a good start code, a new DATA headeris generated when data (not rubbish) starts arriving.

[1757] B.1.2.7 Data Stream Reconstructor (sctokrec.sch, sctokrem.M)

[1758] The Data Stream reconstructor has two-wire interface inputs: onefrom scinshift for bypassed tokens, and one from scoshift for packeddata and start codes. Switching between the two sources is only allowedwhen the current token (from either source) has been completed (lowextension bit arrived).

[1759] B.1.2.8 Start Value to Start Number Conversion (scdromhw.sch,schrom.M)

[1760] The process of converting start values into tokens is done in twostages. This block deals mainly with coding standard dependent issuesreducing the 520 odd potential codes down to 16 coding standardindependent indices.

[1761] As mentioned earlier, start values (including JPEG ones) aredistinguished from all other data by a flag (value_not_token) If v_not_tis high, this block converts the 4 or 8 bit value, depending on theCODING_STANDARD, into a 4 bit start_number which is independent of thestandard, and flags any unrecognized start codes.

[1762] The start numbers are as follows: TABLE B.1.2 Start Code numbers(indices) Start/Marker Code Index (start_number) Resulting Tokennot_a_start_code  0 — sequence_start_code  1 SEQUENCE_STARTgroup_start_code  2 GROUP_START picture_start_code  3 PICTURE_STARTslice_start_code  4 SLICE_START user_data_start_code  5 USER_DATAextension_start_code  6 EXTENSION_DATA sequence_end_code  7 SEQUENCE_ENDJPEG Markers DHT  8 DHT DQT  9 DQT DNL 10 DNL DRI 11 DRI JPEG markersthat can be mapped onto tokens for MPEG/H.261 SOS picture_start_codePICTURE_START SOI sequence_start_code SEQUENCE_START EOIsequence_end_code SEQUENCE_END SOF0 group_start_code GROUP_START JPEGmarkers that generate extn or user data JPG extension_start_codeEXTENSION_DATA JPGn extension_start_code EXTENSION_DATA APPnuser_data_start_code USER_DATA COM user_data_start_code USER_DATA

[1763] B.1.2.9 Sart Number to Token Conversion (sconvert.sch,sconverm.M)

[1764] The second stage of the conversion is where the above startnumbers (or indices) are converted into tokens. This block also handlestoken extensions where appropriate, discarding of eXtension and userdata, and search modes.

[1765] Search modes are a means of entering a data stream at a randompoint. The search mode can be set to one of eight values:

[1766] 0: Normal Operation—find next start code.

[1767] 1/2: System level searches not implemented on Spatial Decoder

[1768] 3: Search for Sequence or higher

[1769] 4: Search for group or higher

[1770] 5: Search for picture or higher

[1771] 6: search for slice or higher

[1772] 7: Search for next start code

[1773] Any non-zero search mode causes data to be discarded until thedesired start code (or higher in the syntax) is detected.

[1774] This block also adds the token extensions to PICTURE and SLICEstart tokens:

[1775] PICTURE_START is extended with PICTURE_NUMBER, a four bit countof pictures.

[1776] SLICE_START is extended with svp (slice vertical position). Thisis the “value” of the start code minus one (MPEG, H.261), and minus OXDO(JPEG).

[1777] B.1.2.10 Data Stream Formatting (scinsert.sch, scinserx.M)

[1778] In the present invention, Data Stream Formatting relates toconditional insertion of PICTURE_END, FLUSH, CODING_STANDARD,SEQUENCE_START tokens, and generation of the STOP_AFTER_PICTURE event.Its function is best simplified and described in software: switch(input_data) case (FLUSH) 1. if (in_picture) output = PICTURE_END 2.output = FLUSH 3. if (in_picture & stop_after_picture) sap_error = HIGHin_picture = FALSE; 4. in_picture = FALSE; break case(SEQUENCE_START) 1. if (in_picture) output = PICTURE_END 2. if(in_picture & stop_after_picture) 2a. output = FLUSH 2b. sap_error =HIGH in_picture = FALSE 3. output = CODING_STANDARD 4. output = standard5. output = SEQUENCE_START 6. in_picture = FALSE; break case(SEQUENCE_END) case (GROUP_START): 1. if (in_picture) output =PICTURE_END 2. if (in_picture & stop_after_picture) 2a. output = FLUSH2b. sap_error = HIGH in_picture = FALSE 3. output = SEQUENCE_END orGROUP_START 4. in_picture = FALSE; break case (PICTURE_END) 1. output =PICTURE_END 2. if (stop_after_picture) 2a. output = FLUSH 2b. sap_error= HIGH 3. in_picture = FALSE break case (PICTURE_START) 1. if(in_picture) output = PICTURE_END 2. if (in_picture &stop_after_picture) 2a. output = FLUSH 2b. sap_error = HIGH 3. if(insert_sequence_start) 3a. output = CODING_STANDARD 3b. output =standard 3c. output = SEQUENCE_START insert_sequence_start = FALSE 4.output = PICTURE_START in_picture = TRUE break default: Just pass itthrough

[1779] SECTION B.2 Huffman Decoder and Parser

[1780] B.2.1 Introduction

[1781] This section describes the Huffman Decoder and Parser circuitryin accordance with the present invention.

[1782]FIG. 118 shows a high level-block diagram of the Huffman Decoderand Parser. Many signals and buses are omitted from this diagram in theinterests of clarity, in particular, there are several places where datais fed backwards (within the large loop that is shown).

[1783] In essence, the Huffman Decoder and Parser of the presentinvention consist of a number of dedicated processing blocks (shownalong the bottom of the diagram) which are controlled by a programmablestate machine.

[1784] Data is received from the Coded Data Buffer by the “Inshift”block. At this point, there are essentially two types of informationwhich will be encountered: Coded data which is carried by DATA Tokensand start codes which have already been replaced by their respectiveTokens by the Start Code Detector. It is possible that other Tokens willbe encountered but all Tokens (other than the DATA Tokens) are treatedin the same way. Tokens (start codes) are treated as a special case asthe vast majority of the data will still be encoded (in H.261, JPEG orMPEG).

[1785] In the present invention, all data which is carried by the DATATokens is transferred to the Huffman Decoder in a serial form(bit-by-bit). This data, of course, includes many fields which are notHuffman coded, but are fixed length coded. Nevertheless, this data isstill passed to the Huffman Decoder serially. In the case of Huffmanencoded data, the Huffman Decoder only performs the first stage ofdecoding in which the actual Huffman code is replaced by an indexnumber. If there are N district Huffman codes in the particular codetable which is being decoded, then this “Huffman Index” lies in therange 0 to N-1. Furthermore, the Huffman Decoder has a “no op”, i.e.,“no operation” mode, which allows it to pass along data or tokeninformation to a subsequent stage without any processing by the HuffmanDecoder.

[1786] The Index to Data Unit is a relatively simple block of circuitrywhich performs table look-up operations. It draws its name from thesecond stage of the Huffman decoding process in which the index numberobtained in the Huffman Decoder is converted into the actual decodeddata by a simple table look-up. The Index to Data Unit cooperates withthe Huffman Decoder to act as a single logical unit.

[1787] The ALU is the next block and is provided to implement othertransformations on the decoded data. While the Index to Data Unit issuitable for relatively arbitrary mappings, the ALU may be used wherearithmetic is more appropriate. The ALU includes a register file whichit can manipulate to implement various parts of the decoding algorithms.In particular, the registers which hold vector predictions and DCpredictions are included in this block. The ALU is based around a simpleadder with operand selection logic. It also includes dedicated circuitryfor sign-extension type operations. It is likely that a shift operationwill be implemented, but this will be performed in a serial manner;there will be no barrel shifter.

[1788] The Token Formatter, in accordance with the present invention, isthe last block in the Video Parser and has the task of finallyassembling decoded data into Tokens which can be passed onto the rest ofthe decoder. At this point, there are as many Tokens as will ever beused by the decoder for this particular picture.

[1789] The Parser State Machine, which is 18 bits wide and has beenadopted for use with a two-wire interface has the task of coordinatingthe operation of the other blocks. In essence, it is a very simple statemachine and it produces a very wide “micro-code” control word which ispassed to the other blocks. FIG. 118 shows that the instruction word ispassed from block-to-block by the side of the data. This is, indeed, thecase and it is important to understand that transfers between thedifferent blocks are controlled by two-wire interfaces.

[1790] In the present invention, there is a two-wire interface betweeneach of the blocks in the Video Parser. Furthermore, the Huffman Decoderworks with both serial, data, the inshifter inputs data one bit at atime, and with control tokens. Accordingly, there are two modes ofoperation. If data is coming into the Huffman Decoder via a DATA Token,then it passes through the shifter one bit at a time. Again, there is atwo-wire interface between the inshifter and the Huffman Decoder. Othertokens, however, are not shifted in one bit at a time (serial) butrather in the header of the token. If a DATA token is input, then theheader containing the address information is deleted and the datafollowing the address is shifted in one bit at a time. If it is not aDATA Token, then the entire token, header and all, is presented to theHuffman Decoder all at once.

[1791] In the present invention, it is important to understand that thetwo-wire interface for the Video Parser is unusual in that it has twovalid lines. One line is valid serially and one line is valid tokenly.Furthermore, both lines may not be asserted at the same time. One or theother may be asserted or if no valid data exists, then neither may beasserted although there are two valid lines, it should be recognizedthat there is only a single accept wire in the other direction. However,this is not a problem. The Huffman Decoder knows whether it wants serialdata or token information depending on what needs to be done next basedupon the current syntax. Hence, the valid and accept signals are setaccordingly and an Accept is sent from the Huffman Decoder to theinshifter. If the proper data or token is there, then the inshiftersends a valid signal.

[1792] For example, a typical instruction might decode a Huffman code,transform it in the Index to Data Unit, modify that result in the ALUand then this result is formed into a Token word. A single microcodeinstruction word is produced which contains all of the information to dothis. The command is passed directly to the Huffman Decoder whichrequests data bits one-by-one from the “Inshift” block until it hasdecoded a complete symbol. Control Tokens are input in parallel. Oncethis occurs, the decoded index value is passed along with the originalmicrocode word to the Index to Data Unit. Note that the Huffman Decoderwill require several cycles to perform this operation and, indeed, thenumber of cycles is actually determined by the data which is decoded.The Index to Data Unit will then map this value using a table which isidentified in the microcode instruction word. This value is again passedonto the next block, the ALU, along with the original microcode word.Once the ALU has completed the appropriate operation (the number ofcycles may again be data dependent) it passes the appropriate data ontothe Token Formatting block along with the microcode word which controlsthe way in which the Token word is formed.

[1793] The ALU has a number of status wires or “condition codes” whichare passed back to the Parser State Machine. This allows the StateMachine to execute conditional jump instructions. In fact, allinstructions are conditional jump instructions; one of the conditionsthat may be selected is hard-wired to the value “False”. By selectingthis condition, a “no jump” instruction may be constructed.

[1794] In accordance with the present invention, the Token Formatter hastwo inputs: a data field from the ALU and/or a constant field comingfrom the Parser State Machine. In addition, there is an instruction thattells the Token Formatter how many bits to take from one source and thento fill in with the remaining bits from the other for a total of 8 bits.For example, HORIZONTAL_SIZE has an 8 bit field that is an invariantaddress identifying it as a HORIZONTAL_SIZE Token. In this case, the 8bits come from the constant field and no data comes from the ALU. If,however, it is a DATA Token, then you would likely have 6 bits from theconstant field and two lower bits indicating the color components fromthe ALU. Accordingly, the Token Formatter takes this information andputs it into a token for use by the rest of he system. Note that thenumber of bits from each source in the above examples are merely forillustration purposes and one of ordinary skill in the art willappreciate that the number of bits from either source can vary.

[1795] The ALU includes a bank of counters that are used to countthrough the structure of the picture. The dimensions of the picture areprogrammed into registers associated with the counters that appear tothe “microprogrammer” as part of the register bank. Several of thecondition codes are outputs from this counter bank which allowsconditional jumps based on “start of picture”, “start of macroblock” andthe like.

[1796] Note that the Parser State Machine is also referred to as the“Demultiplex State Machine”. Both terms are used in this document.

[1797] Input Shifter

[1798] In the present invention, the Input Shifter is a very simplepiece of circuitry consisting of a two pipeline stage datapath (“hfidp”)and controlling Zcells (“hfi”).

[1799] In the first pipeline stage, Token decoding takes place. At thisstage, only the DATA token is recognized. Data contained in a DATA tokenis shifted one bit at a time into the Huffman Decoder. The secondpipeline stage is the shift register. In the very last word of a DATAtoken, special coding takes place such that it is possible to transmitan arbitrary number of bits through the coded data buffer. The followingare all possible patterns in the last data word. TABLE B.2.1 Possib1ePatterns in the Last Data Word E D C B A 9 8 7 6 5 4 3 2 1 0 No. of Bits0 1 1 1 1 1 1 1 1 1 1 1 1 1 1 None x 0 1 1 1 1 1 1 1 1 1 1 1 1 1 1 x x 01 1 1 1 1 1 1 1 1 1 1 1 2 x x x 0 1 1 1 1 1 1 1 1 1 1 1 3 x x x x 0 1 11 1 1 1 1 1 1 1 4 x x x x x 0 1 1 1 1 1 1 1 1 1 5 x x x x x x 0 1 1 1 11 1 1 1 6 x x x x x x x 0 1 1 1 1 1 1 1 7 x x x x x x x x 0 1 1 1 1 1 18 x x x x x x x x x 0 1 1 1 1 1 9 x x x x x x x x x x 0 1 1 1 1 10 x x xx x x x x x x x 0 1 1 1 11 x x x x x x x x x x x x 0 1 1 12 x x x x x xx x x x x x x 0 1 13 x x x x x x x x x x x x x x 0 14

[1800] As the data bits are shifted left, one by one, in the shiftregister, the bit pattern “0 followed by all ones” is looked for(padding). This indicates that the remaining bits in the shift registerare no t valid and they are discarded. Note that this action only takesplace in the last word of a DATA Token.

[1801] As described previously, all other Tokens are passed to theHuffman Decoder in parallel. They are still loaded into the secondpipeline stage, but no shifting takes place. Note that the DATA headeris discarded and is not passed to the Huffman at all. Two “valid” wires(out_valid and serial_valid) are provided. only one is asserted at agiven time and it indicates w hat type of data is being presented atthat moment.

[1802] B.2.2 Huffman Decoder

[1803] The Huffman Decoder has a number of modes of operation. The mostobvious is that it can decode Huffman Codes, turning them into a HuffmanIndex Number. In addition, it can decode fixed length codes of a length(in bits) determined by the instruction word. The Huffman Decoder canalso accept Tokens from the Inshift block.

[1804] The Huffman Decode includes a very small state machine. This isused when decoding block-level information. This is because it takes toolong for the Parser State Machine to make decisions (since it must waitfor data to flow through the Index to Data Unit and the ALU before itcan make a decision about that data and issue a new command). When thisState Machine is used, the Huffman Decoder itself issues commands to theIndex to Data Unit and ALU. The Huffman Decoder State Machine cannotcontrol all of the microcode instruction bits and, therefore, it cannotissue the full range of commands to the other blocks.

[1805] B.2.2.1 Theory of Operation

[1806] When decoding Huffman codes, the Huffman Decoder of the presentinvention uses an arithmetic procedure to decode the incoming code intoa Huffman Index Number. This number lies between 0 and N-1 (for a codetable that has N entries). Bits are accepted one by one from the Inputshifter.

[1807] In order to control the operation of the machine, a number oftables are required. These specify for each possible number of bits in acode (1 to 16 bits) how many codes there are of that length. Asexpected, this information is typically not sufficient to specify ageneral Huffman code. However, in MPEG, H.261 and JPEG, the Huffmancodes are chosen such that this information alone can specify theHuffman Code table. There is unfortunately just one exception to this;the Tcoefficient table from H.261 which is also used in MPEG. Thisrequires an additional table that is described elsewhere (the exceptionwas deliberately introduced in H.261 to avoid start code emulation).

[1808] It is important to realize that the tables used by this HuffmanDecoder are precisely the same as those transmitted in JPEG. This allowsthese tables to be used directly while other designs of Huffman decoderswould have required the generation of internal tables from thetransmitted ones. This would have required extra storage and extraprocessing to do the conversion. Since the tables in MPEG and H.261(with the exception noted above) can be described in the same way, amulti-standard decoder becomes practical.

[1809] The following fragment of “C” illustrates the decoding process;int total = 0; int s = 0; int bit = 0; insigned long code = 0; int index= 0; while (index>=total) { if(bit>=max_bits) fall(“huff_decode: ran offend of huff table\n”); code=(code<<1) Inext_bit0; index=code−s+total;total+=codes_per_bit[bit]; s=(s+codes_per_bit[bit])<<1; bit++; }

[1810] The process generally, is directly mapped into the siliconimplementation although advantage is taken of the fact that certainintermediate values can be calculated in clock phases before they arerequired.

[1811] From the code fragment we see that;

total_(n+1)=total_(n) +cpb _(n)  EQ 1.

's_(n+1)=2 ('s_(n) +cpb _(n))  EQ 2.

code_(n+1)=2code_(n)+bit_(n)  EQ 3.

index_(n+1)=2code_(n) +bit_(n)+total_(n) −'s _(n)  EQ 4.

[1812] Unforunately in the hardware i proved easier to use a modifiedset of equations in which a variable “shifted” is use in place of thevariable “s”. In this case;

[1813] In the hardware, however, it proved easier to use a modified setof equations in which a variable “shifted” is used in place of thevariable “s”. In this case;

shifted_(n+1)=2shifted_(n)+cpb_(n)  EQ 5.

[1814] It turns out that:

;_(n)=2shifted_(n)  EQ 6

[1815] and so substituting this back into Equation 4 we see that:

index_(n+1)=2 (code_(n)−shifted_(n))+total_(n)+bit_(n)  EQ 7.

[1816] In addition to calculating successive values of “index”, it isnecessary to know when the calculation is completed. From the “C” codefragment we see that we are done when:

index_(n+1<total) _(n+1)  EQ 8.

[1817] Substituting from Equation 7 and Equation 1 we see that we aredone when:

2(code_(n)−shifted_(n))+bit_(n) −cpb _(n)<0  EQ 9

[1818] In the hardware implementation of the present invention, thecommon term in Equation 7 and Equation 9, (code_(n)−shifted_(n)) iscalculated one phase before the remainder of these equations areevaluated to give the final result and the information that thecalculation is “done”.

[1819] One word of warning. In various pieces of “C” code, notably thebehavioral compiled code Huffman Decoder and the sm4code projects, the“C” fragment is used almost directly, but the variable “s” is actuallycalled 'shifted”. Thus, there are two different variables called“shifted”. One in the “C” code and the other in the hardwareimplementation. These two variables differ by a factor of two.

[1820] B.2.2.1.1 Inverting the Data Bits

[1821] There is one other piece of information required to correctlydecode the Huffman codes. This is the polarity of the coded data. Itturns out that H.261 and JPEG use opposite conventions. This reflectsitself in the fact that the start codes in H.261 are zero bits whilstthe marker bytes in JPEG are one bits.

[1822] In order to deal with both conventions, it is necessary to invertthe coded data bits as they are read into the Huffman Decoder in orderto decode H.261 style Huffman codes. This is done in the obvious mannerusing an exclusive OR gate. Note that the inversion is only performedfor Huffman codes, as when decoding fixed length codes, the data is notinverted.

[1823] MPEG uses a mix of the two conventions. In those aspectsinherited from H.261, the H.261 convention is used. In those inheritedfrom JPEG (the decoding of DC intra coefficients) the JPEG conventionisused.

[1824] B.2.2.1.2 Transform Coefficients Table

[1825] When using the transform coefficients table in H.261 and MPEG,there are number of anomalies. First, the table in MPEG is a super-setof the table in H.261. In the hardware implementation of the presentinvention, there is no distinction drawn between the two standards andthis means that an H.261 stream that contains codes from the extendedpart of the table (i.e., MPEG codes) will be decoded in the “correct”manner. Of course, other aspects of the compression standard may well bebroken. For example, these extended codes will cause start codeemulation in H.261.

[1826] Second, the transform coefficient table has an anomaly that meansthat it is not describable in the normal manner with the codes_per_bittables. This anomaly occurs with the codes of length six bits. Thesecode words are systematically substituted by alternate code words. In anencoder, the correct result is obtained by first encoding in the normalmanner. Then, for all codes that are six bits or longer, the first sixbits are substituted by another six bits by a simple table look-upoperation. In a decoder, in accordance with the present invention, thedecoding process is interrupted just before the sixth bit is decoded,the code words are substituted using a table look-up, and the decodingcontinues.

[1827] In this case, there are only ten possible six-bit codes so thenecessary look-up table is very small. The operation is further helpedby the fact that the upper two bits of the code are unaltered by theoperation. As a result, it is not necessary to use a true look-up table.Instead a small collection of gates are hard-wired to give theappropriate transformation. The module that does this is called,“hftcfrng”. This type of code substitution is defined herein as a “ring”since each code from the set of possible codes is replaced by anothercode from that set (no new codes are introduced or old codes omitted).

[1828] Furthermore, a unique implementation is used for the very firstcoefficient in a block. In this case, it is impossible for anend-of-block code to occur and, therefore, the table is modified so thatthe most commonly occurring symbol can use the code that would otherwisebe interpreted as end-of-block. This may save one bit. It turns out thatwith the architecture for decoding, in accordance with the presentinvention, this is easily accommodated. In short, for the first bit ofthe first coefficient the decoding is deemed “done” if “index” has thevalue zero. Furthermore, after decoding only a single bit there are onlytwo possible values for “index”, zero and one, it is only necessary totest one bit.

[1829] B.2.2.1.3 Register and Adder Size

[1830] The Huffman Decoder of the present invention can deal withHuffman codes that may be as long as 16 bits. However, the decodingmachine is only eight bits wide. This is possible because we know thatthe largest possible value of the decoded Huffman Index number is 255.In fact, this could only happen in extended JPEG and, in the currentapplication, the limit is somewhat lower (but larger than 128, so 7 bitswill not suffice).

[1831] It turns out that for all legal Huffman codes, not only the finalvalue of “index”, but all intermediate values lie in the range 0 to 255.However, for an illegal code, i.e., an attempt to decode a code that isnot in the current code table (probably due to a data error) the indexvalue may exceed 255. Since we are using an eight bit machine, it ispossible that at the end of decoding, the final value of “index” doesnot exceed 255 because the more significant bits that tell us an errorhas occurred have been discarded. For this reason, if at any time duringdecoding the index value exceeds 255 (i.e., carry out of the adder thatforms index) an error occurs and decoding is abandoned.

[1832] Twelve bits of “code” are preserved. This is not necessary fordecoding Huffman codes where an eight bit register would have beensufficient. These upper bits are required for fixed length codes whereup to twelve bits may be read.

[1833] B.2.2.1.4 Operation for Fixed Length Codes

[1834] For fixed length codes, the “codes per bit” value is forced tozero. This means that “total” and “shifted” remain at zero throughoutthe operation and “index” is, therefore, the same as code. In fact, theadders and the like only allow an eight bit value to be produced for“index”. Because of this, the upper bits of the output word are takendirectly from the “code” register when decoding fixed length codes. Whendecoding Huffman codes these upper bits are forced to zero.

[1835] The fact that sufficient bits have been read from the input iscalculated in the obvious manner. A comparator compares the desirednumber of bits with the “bit” counter.

[1836] B.2.2.2 Decoding Coefficient Data

[1837] The Parser State Machine, in accordance with the presentinvention, is generally only used for fairly high-level decoding. Thevery lowest level decoding within an eight-by-eight block of data is notdirectly handled by this state machine. The Parser State Machine gives acommand to the Huffman Decoder of the form “decode a block”. The HuffmanDecoder, Index to Data Unit and ALU work together under the control of adedicated state machine (essentially in the Huffman Decoder). Thisarrangement allows very high performance decoding of entropy codedcoefficient data. There are also other feedback paths operational inthis mode of operation. For instance, in JPEG decoding where the VLCsare decoded to provide SIZE and RUN information, the SIZE information isfed back directly from the output of the Index to Data Unit to theHuffman Decoder to instruct the Huffman Decoder how many FLC bits toread. In addition, there are several accelerators implemented. Forinstance, using the same example all VLC values which yield a SIZE ofzero are explicitly trapped by looking at the Huffman Index Value beforethe Index to Data stage. This means that in the case of non-zero SIZEvalues, the Huffman Decoder can proceed to read one FLC bit BEFORE theactual value of SIZE is known. This means that no clock cycles arewasted because this reading of the first FLC bit overlaps the singleclock cycle required to perform the table look-up in the Index to DataUnit.

[1838] B.2.2.2.1 MPEG and H.261 AC Coefficient Data

[1839]FIG. 127 shows the way in which AC Coefficients are decoded inMPEG and H.261. A flow chart detailing the operation of the HuffmanDecoder is given in FIG. 119.

[1840] The process starts by reading a VLC code. In the normal course ofevents, the Huffman index is mapped directly into values representingthe six bit RUN and the absolute value of the coefficient. A one bit FLCis then read giving the sign of the coefficient. The ALU assembles theabsolute value of the coefficient with this sign bit to provide thefinal value of the coefficient.

[1841] Note that the data format at this point is sign-magnitude and,therefore, there is little difficulty in this operation. The RUN valueis passed on an auxiliary bus of six bits while the coefficients value(LEVEL) is passed on the normal data bus.

[1842] Two special cases exist and these are trapped by looking at thevalue of the decoded index before the Index to Data operation. These areEnd of Block (EOB) and Escape coded data. In the case of EOB, the factthat this occurred is passed along through the Index to Data Unit andthe ALU blocks so that the Token Formatter can correctly close the openDATA Token.

[1843] Escape coded data is more complicated. First six bits of RUN areread and these are passed directly through the Index to Data Unit andare stored in the ALU. Then, one bit of FLC is read. This is the mostsignificant bit of the eight bits of escape that are described in MPEGand H.261 and it gives the sign of the level. The sign is explicitlyread in this implementation because it is necessary to send differentcommands to the ALU for negative values versus positive values. Thisallows the ALU to convert the twos complement value in the bit streaminto sign magnitude. In either case, the remaining seven bits of FLC arethen read. If this has the value zero, then a further eight bits must beread.

[1844] In the present invention, the Huffman Decoder's internal statemachine is responsible for generating commands to control itself and toalso control the Index to Data Unit, the ALU and the Token Formatter. Asshown in FIG. 124, the Huffman Decoder's instruction comes from one ofthree sources, the Parser State Machine, the Huffman State Machine or aninstruction stored in a register that has previously been received fromthe Parser State Machine. Essentially, the original instruction from theParser State Machine (that causes the Huffman State Machine to take overcontrol and read coefficients) is retained in a register, i.e., eachtime a new VLC is required, it is used. All the other instructions forthe decoding are supplied by the Huffman State Machine.

[1845] B.2.2.2.2 MPEG DC Coefficient Data

[1846] This is handled in the same way as JPEG DC Coefficient Data. Thesame (loadable) tables are used and it is the responsibility of thecontrolling microprocessor to ensure that their contents are correct.The only real difference from the MPEG standard is that the predictorsare reset to zero (like in JPEG) the correction for this being made inthe Inverse Quantizer.

[1847] B.2.2.2.3 JPEG Coefficient Data

[1848]FIG. 120 is a block diagram illustrating the hardware, inaccordance with the present invention, for decoding JPEG ACCoefficients. Since the process for DC Coefficients is essentially asimplication of the JPEG process, the diagram serves for both AC and DCCoefficients. The only real addition to the previous diagram for theMPEG AC coefficients is that the “SSSS” field is fed back and may beused as part of the Huffman Decoder command to specify the number of FLCbits to be read. The remainder of the command is supplied by the HuffmanState Machine.

[1849]FIG. 121 depicts flow charts for the Huffman decoding of both ACand DC Coefficients.

[1850] Dealing first with the process for AC Coefficients, the processstarts by reading a VLC using the appropriate tables (there are two ACtables). The Huffman index is then converted into the RUN and SIZEvalues in the Index to Data Unit. Two values are trapped at the HuffmanIndex stage, these are for EOB and ZRL. These are the only two valuesfor which no FLC bits are read. In the case when the decode index isneither of these two values, the Huffman Decoder immediately reads onebit of FLC while it waits for the Index to Data Unit to complete thelook-up operation to determine how many bits are actually required. Inthe case of EOB, no further processing is performed by the Huffman StateMachine in the Huffman Decoder and another command is read from theParser State Machine.

[1851] In the case of ZRL, no FLC bits are required but the block is notcompleted. In this case, the Huffman decoder immediately commencesdecoding a further VLC (using the same table as before).

[1852] There is a particular problem with detecting the index valuesassociated with ZRL and EOB. This is because (unlike H.261 and MPEG) theHuffman tables are downloadable. For each of the two JPEG AC tables, tworegisters are provided (one for ZRL and one for EOB). These are loadedwhen the table is downloaded. They hold the value of index associatedwith the appropriate symbol.

[1853] The ALU must convert the SIZE bit FLC code to the appropriatesign-magnitude value. These are loaded when the table is downloaded.They hold the value of index associated with the appropriate symbol.

[1854] The ALU must convert the SIZE bit FLC code to the appropriatesign-magnitude value. This can be done by first sign-extending the valuewith the wrong sign. If the sign bit is now set, then the remaining bitsare inverted (ones complement).

[1855] In the case of DC Coefficients, the decision making in theHuffman Decoding Stage is somewhat easier because there is no equivalentof the ZRL field. The only symbol which causes zero FLC bits to be readis the one indicating zero DC difference. This is again trapped at theHuffman Index stage, a register being provided to hold this index foreach of the (downloadable) JPEG DC tables.

[1856] The ALU of the present invention has the job of forming the finaldecoded DC coefficient by retaining a copy of the last DC Coefficientvalue (known as the prediction). Four predictors are required, one foreach of the four active color components. When the DC difference hasbeen decoded, the ALU adds on the appropriate predictor to form thedecoded value. This is stored again as the predictor for the next DCdifference of that color component. Since DC coefficients are signed(because of the DC offset) conversion from twos complement to signmagnitude is required. The value is then output with a RUN of zero. Infact, the instructions to perform some of the last stages of this arenot supplied by the Huffman State Machine. They are simply executed bythe Parser State Machine.

[1857] In a similar manner to the AC Coefficients, the ALU must firstform the DC difference from the SIZE bits of FLC. However, in this case,a twos complement value is required to be added to the predictor. Thiscan be formed by first sign extending with the wrong sign, as before. Ifthe result is negative, then one must be added to form the correctvalue. This can, of course, be added at the same time as the predictorby jamming the carry into the adder.

[1858] B.2.2.3 Error Handling

[1859] Error handling deserves some mention. There are effectively foursources of error that are detected:

[1860] Ran off the end of a table.

[1861] Serial when token expected.

[1862] Token when serial expected.

[1863] Too many coefficients in a block.

[1864] The first of these occurs in two situations. If the bit counterreaches sixteen (legal values being 0 to 15) then an error has occurredbecause the longest legal Huffman code is sixteen bits. If anyintermediate value of “index” exceeds 255 then an error has occurred asdescribed in section B.2.2.1.3.

[1865] The second occurs when serial data is encountered when a Tokenwas expected. The third when the opposite condition arises.

[1866] The last type of error occurs if there are too many coefficientsin a block. This is actually detected in the Index to Data Unit.

[1867] When any of these conditions arises, the error is noted in theHuffman error register and the Parser state machine is interrupted. Itis the responsibility of the Parser State Machine to deal with the errorand to issue the commands necessary to recover.

[1868] The Huffman cooperates with the Parser State Machine at the timeof the interrupt in order to assure correct operation. When the HuffmanDecoder interrupts the Parser State Machine, it is possible that a newcommand is waiting to be accepted at the output of the Parser StateMachine. The Huffman Decoder will not accept this command for two wholecycles after it has interrupted the Parser State Machine. This allowsthe Parser State Machine to remove the command that was there (whichshould not now be executed) and replace it with an appropriate one.After these two cycles, the Huffman Decoder will resume normal operationand accept a command if a valid command is there. If not, then it willdo nothing until the Parser State Machine presents a valid command.

[1869] When any of these errors occur, the “Huffman Error” event bit isset and, if the mask bit is set, the block will stop and the controllingmicroprocessor will be interrupted in the normal manner.

[1870] One complication occurs because in certain situations, what lookslike an error, is not actually an error. The most important place wherethis occurs is when reading the macroblock address. It is legal in thesyntaxes of MPEG, H.261 and JPEG for a Token to occur in place of theexpected macroblock address. If this occurs in a legal manner, theHuffman error register is loaded with zero (meaning no error) but theParser State Machine is still interrupted. The Parser State Machine'scode must recognize this “no error” situation and respond accordingly.In this case, the “Huffman Error” event bit will not be set and theblock will not stop processing.

[1871] Several situations must be dealt with. First, the Token occursimmediately with no preceding serial bits. In this case, a “Token whenserial expected error” would occur. Instead, a “no error” error occursin the way just described.

[1872] Second, the Token is preceded by a few serial bits. In this case,a decision is made. If all of the bits preceding the Token had the valueone (remember that in H.261 and MPEG the coded data is inverted so theseare zero bits in the coded data file) then no error occurs. If, however,any of them were zero, then they are not valid stuffing bits and, thus,an error has occurred and a “Token when serial expected” error doesoccur.

[1873] Third, the token is preceded by many bits. In this case, the samedecision is made. If all sixteen bits are one, then they are treated aspadding bits and a “fno error” error occurs. If any of them had beenzero, then “Ran off Huffman Table” error occurs.

[1874] Another place that a token may occur unexpectedly is in JPEG.When dealing with either Huffman tables or Quantizer tables, any numberof tables may occur in the same Marker Segment. The Huffman Decoder doesnot know how many there are. Because of this fact, after each table iscompleted it reads another 4-bit FLC assuming it to be a new tablenumber. If, however, a new marker segment starts, then a token will beencountered in place of the 4 bit: FLC. This requirement is not foreseenand, therefore, an “Ignore Errors” command bit has been added.

[1875] B.2.2.4 Huffman Commands

[1876] Here are the bits used by the Parser State Machine to control theHuffman Decoder block and their definitions. Note that the Index to DataUnit command bits are also included in this table. From themicroprogrammer's point of view, the Huffman Decoder and the Index toData Unit operate as one coherent logical block. TABLE B.2.2 HuffmanDecoder Commands Bit Name Function 11 Ignore Errors Used to disableerrors in certain circumstances. 10 Download Either nominate a table fordownload or download data into that table. 9 Alutab Use information fromthe ALU registers to specify the table number (or number of bits of FLC)8 Bypass Bypass the Index to Data Unit 7 Token Decode a Token ratherthan FLC or VLC 6 First Coeff Selects first coefficient tncx for Tcoefftable and other special modes. 5 Special If set the Huffman Statemachine should take over control. 4 VLC (not FLC) Specify VLC or FLC 3Table[3] Specify the table to use for VLC 2 Table[2] or the number ofbits to read for a FLC 1 Table[1] 0 Table[0]

[1877] B.2.2.4.1 Reading FLC

[1878] In this mode, Ignore Errors, Download, Alutab, Token, FirstCoeff, Special and VLC are all zero. Bypass will be set so that no Indexto Data translation occurs.

[1879] The binary number in Table[3:0] indicates how many bits are to beread.

[1880] The numbers 0 to 12 are legal. The value zero does indeed readzero bits (as would be expected) and this instruction is, therefore, theHuffman Decoder NOP instruction. The values 13, 14 and 15 will not workand the value 15 is used when the Huffman State Machine is in control todenote the use of “SSSS” as the number of bits of FLC to read.

[1881] B.2.2.4.2 Reading VLC

[1882] In this mode, Ignore Errors, Download, Alutab, Token, FirstCoefficient and Special are zero and VLC is one. Bypass will usually bezero so that Index to Data translation occurs.

[1883] In this mode Token, First Coefficient and Special are all zero,VLC is one.

[1884] The binary number in Table(3:0) indicates which table to use asshown: TABLE B.2.3 Huffman Tables Table[3:0] VLC Table to use 0000TCoefficient (MPEG and H.261) 0001 CBP (Coded Block Pattern) 0010 MBA(Macroblock Address) 0011 MVD (Motion Vector Data) 0100 Intra Mtype 0101Predicted Mtype 0110 Interpolated Mtype 0111 H.261 Mtype 10x0 JPEG(MPEG) DC Table 0 10x1 JPEG (MPEG) DC Table 1 11x0 JPEG AC Table 0 11x1JPEG AC Table 1

[1885] Note that in the case of the tables held in RAM (i.e., the JPEGtables) bit 1 is not used so that the table selections occur twice. if anon-baseline JPEG decoder is built, then there will be four DC tablesand four AC tables and Tables [1] will then be required.

[1886] If Tables[3] is zero, then the input data is inverted as it isused in order that the tables are read correctly as H.261 style tables.In the case of Table(3:0]=0, the appropriate Ring modification is alsoapplied.

[1887] B.2.2.4.3 NOP Instruction

[1888] As previously described, the action of reading a FLC of zero bitsis used as a No Operation instruction. No data is read from the inputports (either Token or Serial) and the Huffman Decoder outputs a datavalue of zero along with the instruction word.

[1889] B.2.2.4.4 TCoefficient First Coefficient

[1890] The H.261 and MPEG TCoefficient Table has a special non-Huffmancode that is used for the very first coefficient in the block. In orderto decode a TCoefficient at the start of a block, the First Coefficientbit may be set along with a VLC instruction with table zero. One of themany effects of the First Coefficient bit is to enable this code to bedecoded.

[1891] Note that in normal operation, it is unusual to issue a “simple”command to read a TCoefficient VLC. This is because control is usuallyhanded to the Huffman Decoder by setting the Special Bit.

[1892] B.2.2.4.5 Reading Token Words

[1893] In order to read Token words, the Token bit should be set to one.The Special and First Coefficient bits should be zero. The VLC bitshould also be set if the Table[0] bit is to work correctly.

[1894] In this mode, the bits Table[1] and Table[0] are used to modifythe behavior of the Token reading as follows: Bit Meaning Table[0]Discard padding bits of serial data Table[1] Discard all serial data.

[1895] If both Table[0] and Table[1] are zero, then the presence ofserial data before the token is considered to be an error and will besignalled as such.

[1896] If Table [1] is set, then all serial data is discarded until aToken Word is encountered. No error will be caused by the presence ofthis serial data.

[1897] If Table[0] is set, then padding bits will be discarded. It is,of course, necessary to know the polarity of the padding bits. This isdetermined by Table[3] in exactly the same way as for reading VLC data.If Table [3] is zero, input data is first inverted and then any “one”bits are discarded. If Table [3] is set to one, the input data is NOTinverted and “one” bits are discarded. Since the action of inverting thedata depending upon the Table[3] bit is conditional on the VLC bit, thisbit must be set to one. If any bits that are not padding bits areencountered (i.e., “1” bits in H.261 and MPEG) an error is reported.

[1898] Note that in these instructions only a single Token word is read.The state of the extension bit is ignored and it is the responsibilityof the Demux to test this bit and act accordingly. Instructions to readmultiple words are also provided—see the section on SpecialInstructions.

[1899] B.2.2.4.6 ALU Registers Specify Table

[1900] If the “Alutab” bit is set, registers in the ALU's register filecan be used to determine the actual table number to use. The tablenumber supplied in the command, together with the VLC bit, determineswhich ALU registers are used; TABLE B.2.4 ALU Register Selection VLCtable[3:0] ALU table 0 x0xx fwd_r_size 0 x1xx bwd_r_size 1 x0xxdc_huff[compid] 1 x1xx ac_huff[compid]

[1901] In the case of fixed length codes, the correct number of bits areread for decoding the vectors. If r_size is zero, a NOP instructionresults.

[1902] In the case of Huffman codes, the generated table number hastable[3] set to one so that the resulting number refers to one of theJPEG tables.

[1903] B.2.2.4.7 Special Instructions

[1904] All of the instructions (or modes of operation) described thusfar are considered as “Simple” instructions. For each command that isreceived, the appropriate amount of input data (of either serial oftoken data) is read and the resulting data is output. If no error isdetected, exactly one output will be generated per command.

[1905] In the present invention, special instructions have thecharacteristic that more than one output word may be generated for asingle command. In order to accomplish this function, the HuffmanDecoder's internal State Machine takes control and will issue itselfinstructions as required until it decides that the instruction which theParser requested has been complete.

[1906] In all Special instructions, the first real instruction of thesequence that is to be executed is issued with the Special bit set toone. This means that all sequences must have a unique first instruction.The advantage of this scheme is that the first real instruction of thesequence is available without a look-up operation being required basedupon the command received from the Parser.

[1907] There are four recognized special instructions:

[1908] TCoefficient

[1909] JPEG DC

[1910] JPEG AC

[1911] Token

[1912] The first of these reads H.261 and MPEG Transform coefficients,and the like, until the end-of-block symbol is read. If the block is anon-intra block, this command will read the entire block. In this case,the “First Coefficient” bit should be set so that the first coefficienttrick is applied. If the block is an intra block, the DC term shouldalready have been read and the “First Coefficient” bit should be zero.

[1913] In the case of an intra block in H.261, the DC term is read usinga “simple” instruction to read the 8 bits FLC value. In MPEG, the “JPEGDC” special instruction described below is used.

[1914] The “JPEG DC” command is used to read a JPEG style DC term(including the SSSS bits FLC indicated by the VLC). It is also used inMPEG. The First Coefficient bit must be set in order that a counter(counting the number of coefficients) in the Index to Data Unit isreset.

[1915] The “JPEG AC” command is used to read the remainder of a block,after the DC term until either an EOB is encountered or the 64^(th)coefficient is read.

[1916] The “Token” command is used to read an entire Token. Token wordsare read until the extension bit is clear. It is a convenient method ofdealing with unrecognized tokens.

[1917] B.2.2.4.8 Downloading Tables.

[1918] In the present invention, the Huffman Decoder tables can bedownloaded by using the “Download” bit. The first step is to nominatewhich table to download. This is done by issuing a command to read a FLCwith both the Download and First Coeff bits set. This is treated as anNOP so no bits are actually read, but the table number is stored in aregister and is used to identify which table is being loaded insubsequent downloading. TABLE B.2.5 JPEG Tables table[3:0] Tablenominated 10xx JPEG DC Codes per bit 11xx JPEG AC Codes per bit 00xxJPEG DC Index to Data 01xx JPEG AC Index to Data

[1919] As the above table shows, either the AC or DC tables can beloaded and table[3] determines whether it is the codes-per-bit table (inthe Huffman decoder itself) or the Index to Data table that is loaded.

[1920] Once the table is nominated, data is downloaded into it byissuing a command to read the required number of FLC (always 8 bits)with the Download bits set (and the First Coeff bit zero). This causesthe decoded data to be written into the nominated table. An addresscounter is maintained, the data is written at the current address andthen the address counter is incremented. The address counter is reset tozero whenever a table is nominated.

[1921] When downloading the Index to Data tables, the data and addressesare monitored. Note that the address is the Huffman Index number whilethe data loaded into that address is the final decoded symbol. Thisinformation is used to automatically load the registers that hold theHuffman index number for symbols of interest. Accordingly, in a JPEG ACtable, when the data has the value corresponding to ZRL is recognized,the current address is written into the register CED_H_KEY_ZRL_INDEX0 orCED_H_KEY_ZRL_INDEX1 as indicated by the table number.

[1922] Since decoded data is written into the codes-per-bit table onephase after it has been decoded, it is not possible to read data fromthe table during this phase. Therefore, an instruction attempting toread a VLC that is issued immediately after a table download instructionwill fail. There is no reason why such a sequence should occur in anyreal application (i.e., when doing JPEG). It is, however, possible tobuild simulation tests that do this.

[1923] B.2.2.5 Huffman State Machine

[1924] The Huffman State Machine, in accordance with the presentinvention, operates to provide the Huffman Decoder commands that areinternally generated in certain cases. All of the commands that may begenerated by the internal state machine may also be provided to theHuffman Decoder by the Demux.

[1925] The basic structure of the State Machine is as follows. When acommand is issued to the Huffman Decoder, it is stored in a series ofauxiliary latches so that it may be reused at a later time. The commandis also executed by the Huffman Decoder and analyzed by the HuffmanState Machine. If the command is recognized as being the first of aknown instruction sequence and the SPECIAL bit is set, then the HuffmanDecoder State Machine takes over control of the Huffman Decoder from theParser State Machine.

[1926] At this point, there are three sources of instructions for theHuffman Decoder:

[1927] 1)The Parser State Machine—this choice is made at the completionof the special instruction (e.g., when EOB has been decoded) and thenext demux command is accepted.

[1928] 2)The Huffman State Machine. The Huffman State Machine mayprovide itself with an arbitrary command.

[1929] 3)The original instruction that was issued by the Parser StateMchine to start the instruction.

[1930] In case (2), it is possible that the table number is provided byfeedback from the Index to Data Unit, this would then replace the fieldin the Huffman State Machine ROM.

[1931] In case (1), in certain instances, table numbers are provided byvalues obtained from the ALU register file (e.g., in the case of AC andDC table numbers and F-numbers). These values are stored in theauxiliary command storage, so that when that command is later reused thetable number is that which has been stored. It is not recovered againfrom the ALU since, in general, the counters will have advanced in orderto refer to the next block.

[1932] Since the choice of the next instruction that will be useddepends upon the data that is being decoded, it is necessary for thedecision to be made very late in a cycle. Accordingly, the generalstructure is one in which all of the possible instructions are preparedin parallel and multiplexing late in the cycle determines the actualinstruction.

[1933] Note that in each case, in addition to determining theinstruction that will be used by the Huffman Decoder in the next cycle,the state machine ROM also determines the instruction that will beattached to the current data as it passes to the Index to Data Unit andthen onto the ALU. In exactly the same way, all three of theseinstructions are prepared in parallel and then a choice is made late inthe cycle.

[1934] Again, there are three choices for this part of the instructionthat correspond to the three choices for the next Huffman Decoderinstruction above.

[1935] 1)A constant instruction suitable for End of Block.

[1936] 2)The Huffman State Machine. The Huffman State Machine mayprovide an arbitrary instruction for the Index to Data Unit.

[1937] 3)The original instruction that was issued by the Parser to startthe instruction.

[1938] B.2.2.5.1 EOB Comparator

[1939] The EOB comparator's output essentially forces selection of theconstant instruction to be presented to the Index to Data Unit and willalso cause the next Huffman Instruction to be the next instruction fromthe Parser. The exact function of the comparator is controlled by bitsin the Huffman State Machine ROM.

[1940] Behind the EOB comparator, there are four registers holding theindex of the EOB symbol in the AC and DC JPEG tables. In the case of theDC tables, there is of course no End-Of-Block symbol but there is thezero-size symbol, that is generated by a DC difference of zero. Sincethis causes zero bits of FLC to be read in exactly the same way as theEOB symbol, they are treated identically.

[1941] In addition to the four index values held in registers, theconstant value, 1, can also be used. This is the index number of the EOBsymbol in H.261 and MPEG.

[1942] B.2.2.5.2 ZRL Comparator

[1943] In the present invention, this is the more general purposecomparator. It causes the choice of either the Huffman State Machineinstruction or the original Instruction for use by the I to D.

[1944] Behind the ZRL comparator, there are four values. Two are inregisters and hold the index of the ZRL code in the AC tables. The othertwo values are constants, one is the value zero and the other is 12 (theindex of ESCAPE in MPEG and H.261).

[1945] The constant zero is used in the case of an FLC. The constant 12is used whenever the table number is less than 8 (and VLC). One of thetwo registers is used if the table number is greater than 7 (and VLC) asdetermined by the low order bit of the table number.

[1946] A bit in the state machine ROM is provided to enable thecomparator and another is provided to invert its action.

[1947] If the TOKEN bit in the instruction is set, the comparator outputis ignored and replaced instead by the extn bit. This allows for runninguntil the end of a Token.

[1948] B.2.5.3 Huffman State Machine ROM

[1949] The instruction fields in the Huffman State Machine are asfollows:

[1950] nxtstate[4:0]

[1951] The address to use in the next cycle. This address may bemodified.

[1952] statectl

[1953] Allows modification of the next state address. If zero, the statemachine address is unmodified, otherwise the LSB of the address isreplaced by the value of either of the two comparators as follows:nxtstate[0] 0 Replace Lsb by EOB match 1 Replace Lsb by ZRL match

[1954] Note: in any case, if the next Huffman Instruction is selected as“Re-run original command” the state machine will jump to location 0, 1,2 or 3 as appropriate for the command.

[1955] eobct[1:0]

[1956] This controls the selection of the next Huffman instruction basedupon the EOB comparator and extn bit as follows: eobctl[1:0] 00 Noeffect - see zrlctl[1:0] 01 Take new (Parser) command if EOB 10 Take new(Parser) command if extn iow 11 Unconditional Demux Instruction

[1957] zrlct[1:0]

[1958] This controls the selection of the next Huffman instruction basedupon the ZRL comparator. If the condition is met, then it takes thestate machine instruction, otherwise it re-runs the originalinstruction. In either case, if an eobctl*+ condition takes a demuxinstruction then this (eobctl*+) takes priority as follows: zrlctl[1:0]00 Never take SM (always re-run) 01 Always take SM command 10 SM if ZRLmatches 11 SM if ZRL does not match

[1959] smtab[3:0]

[1960] In the present invention, this is the table number that will beused by the Huffman Decoder if the selected instruction is the statemachine instruction. However, if the ZRL comparator matches, then thezrltab[3:0] field is used in preference.

[1961] If it is not required that a different table number be useddepending upon whether a ZRL match occurs, then both smtab[3:0] andzrltab{3:0] will have the same value. Note, however, that this can leadto strange simulation problems in Lsim. In the case of MPEG, there is noobvious requirement to load the registers that indicate the Huffmanindex number for ZRL (a JPEG only construction). However, these arestill selected and the output of the ZRL comparator becomes “unknown”despite the fact that both smtab[3:0] and zrltab[3:0] have the samevalue in all cases that the ZRL comparator may be “unknown” (so it doesnot matter which is selected) the next state still goes to “unknown”.

[1962] zrltab[3:0]

[1963] This is the table number that will be used by the Huffman decoderif the selected instruction is the state machine instruction. However,if the ZRL comparator matches then the zritab[3:0] field is used inpreference.

[1964] If it is not required that a different table number be useddepending upon whether a ZRL match occurs, then both smtab[3:0] andzrltab[3:0] will have the same value. Note, however, that this can leadto strange simulation problems in Lsim. In the case of MPEG, there is noobvious requirement to load the register that indicate the Huffman indexnumber for ZRL (a JPEG only construction). However, these are stillselected and the output of the ZRL comparator becomes “unknown” despitethe fact that both smtab[3:0] and zrltab[3:0] have the same value in allcases that the ZRL comparator may be “unknown” (so it does not matterwhich is selected) the next state still goes to “unknown”.

[1965] zrltab[3:0]

[1966] This is the table number that will be used by the Huffman Decoderif the selected instruction is the state machine instruction and the ZRLcomparator matches.

[1967] smvlc

[1968] This is the VLC bits used by the Huffman Decoder if the selectedinstruction is the state machine instruction. aluzrl[1:0]

[1969] This field controls the selection of the instruction that ispassed to the ALU. It will either be the command from the Parser StateMachine (that was stored at the start of the instruction sequence) orthe command from the state machine: aluzrl[1:0] 00 Always take the savedParser State Machine Command 01 Always take the Huffman State MachineCommand 10 Take the Huffman SM command if not EOB 11 Take the Huffman SMcommand if not ZRL

[1970] alueob

[1971] This wire controls modification of the instruction passed to theALU based upon the EOB comparator. This simply forces the ALU's outputmode to “zinput”. This is an arbitrary choice; any output mode apartfrom “none” will suffice. This is to ensure that the end-of-lock commandword is passed to the Token Formatter block where it controls the properformatting of DATA Tokens: alueob 0 Do not modify ALU outsrc field 1Force ‘zinput’ into outsrc if EOB match

[1972] The remainder of the fields are the ALU instruction fields. Theseare properly documented in the ALU description.

[1973] B.2.2.5.4 Huffman State Machine Modification

[1974] In one embodiment of the state machine, the Index to Data Unitneeds to “know” when the RUN part of an escape-coded Tcoefficient isbeing passed to the Index to Data Unit. While this can be accomplishedusing an appropriate bit in the control ROM, but to avoid changing theROM, an alternative approach has been used. In this regard, the addressgoing into the ROM is monitored and the address value five is detected.This is the appropriate location designated in the ROM dealing with theRUN field. Of course, it will be apparent that the ROM could beprogrammed to use other selected address values. Moreover, theaforedescribed approach of using a bit in the control ROM could beutilized.

[1975] B.2.2.6 Guided Tour of Schematics

[1976] In the present invention, the Huffman Decoder is called “hd”.Logically, “hd” actually includes the Index to Data Unit (this isrequired by the limitations of compiled code generation). Accordingly,“hd” includes the following major blocks; TABLE B.2.6 Huffman ModulesModule Name Description hddp Huffman Decoder (Arithmetic) datapathhdstdp Huffman State Machine Datapath hfitod Index to Data Unit

[1977] The following description of the Huffman modules is accomplishedby a global explanation of the various subsystem areas shown in greaterdetail in the drawings which are readily comprehended by one of ordinaryskill in the art.

[1978] B.2.2.6.1 Description of “hd”

[1979] The logic for the two-wire interface control usually includesthree ports controlled by the two-wire interface; data input, dataoutput and the command. In addition, there are two “valid” wires fromthe input shifter; token_valid indicating that a Token is beingpresented on in_data[7:0] and serial_valid indicating that data is beingpresented on serial.

[1980] The most important signals generated are the enables that go tothe latches. The most important being el which is the enable for the ph1latches. The majority of ph0 latches are not enabled whilst two enablesare provided for those that are; e0 associated with serial data and e0tassociated with Token data.

[1981] In the present invention, the “done” signals (done, notdone andtheir ph0 variants done0 and notdone0) indicate when a primitive Huffmancommand is completed. In the case when a Huffman State Machine commandis executed, “done” will be asserted at the completion of each primitivecommand that comprises the entire state-machine command. The signalnotnew prevents the acceptance of a new command from the Parser StateMachine until the entire Huffman State Machine command is completed.

[1982] Regarding control of information received from the Index to DataUnit, the control logic for the “size” field is fed back to the Huffmandecoder during JPEG coefficient decoding. This can actually happen intwo ways. If the size is exactly one, this is fed back on the dedicatedsignal notfbone0. Otherwise, the size is fed back from the output of theIndex to data unit (out_data[3:0] and a signal fbvalid1 indicates thatthis is occurring. The signal muxsize is produced to control themultiplexing of the fed-back data into the command register (sheet 10).

[1983] In addition, there is feedback that exactly 64coefficients havebeen decode. Since in JPEG the EOB is not coded in this situation, thesignal forceeob is produced. By analogy, with the signals for feedingback size, as mentioned above, there are in fact two ways in which thisis done. Either jpegeob is used (a ph1 signal) or jpegeob0. Note that inthe case when a normal feedback is made (jpegeob), the latch i_(—)971 isonly loaded as the data is fed back and not cleared until a new ParserState Machine command is accepted. The signal forceeob does not actuallyget generated until a Huffman code is decoded. Thus, the fixed lengthcode (i.e., size bits) is not affected, but the next Huffman codedinformation is replaced by the forced end of block. In the case whensize is one and jpegeobo is used, only one bit is read and, therefore,i_(—)1255 and i_(—)1256 delay the signal to the correct time. Note thatit is impossible for a size of zero to occur in this situation since theonly symbols with size zero are EOB and ZRL.

[1984] The decoding is fairly random decoding of the command to producetcoeff_tab0 (Huffman decoding using Tcoeff table), mba_tab0 (Huffmandecoding using the MBA table) and nop (no operation). There are severalreasons for generating nop. A Fixed length code of size zero is one, theforceeob signal is another (since no data should be reed from the inputshifter even though an output is produced to signal EOB) and lastlytable download nomination is a third.

[1985] notfrczero (generated by a FLC of size zero, a NOP) ensures thatthe result is zero when a NOP instruction is used. Furthermore, invertindicates when the serial bits should be inverted before Huffmandecoding (see section B.2.2.1.1). ring indicates when the transformcoefficient ring should be applied (see section B.2.2.1.2).

[1986] Decoding is also accomplished regarding addressing thecodes-per-bit ROMs. These are built out of the small data-path ROMs. Thesignals are duplicated (e.g., csha and csla) purely to get sufficientdrive by separating the ROMs into two sections. The address can be takeneither from the bit counter (bit[3:0]) or from the microprocessorinterface address (key-addr[3:0]) depending upon UPI access to the blockbeing selected.

[1987] Additional decoding is concerned with the UPI reading ofregisters such as those that hold the Huffman index values for the JPEGtables (EOB, ZRL etc.). Also included is a tristate driver control forthese registers and the UPI reading of the codes per bit RAMs.

[1988] Arithmetic datapath decoding is also provided for certainimportant bit numbers. first_bit is used in connection with the Tcoefffirst coefficient trick and bit_five is concerned with applying the ringin the Tcoeff table. Note the use of forceeob to simulate the actionthat the EOB comparator matches the decoded index value.

[1989] Regarding the extn bit, if a token is read from the inputshifter, then the associated extn bit is read along with it. Otherwise,the last value of extn is preserved. This allows the testing of the extnbit by the microcode program at any time after a token has been read.

[1990] When zerodat is asserted, the upper four bits of the Huffmanoutput data are forced to zero. Since these only have valid values whendecoding fixed length codes, they are zeroed when decoding a VLC, atoken or when a NOP instruction is executed for any reason.

[1991] Further circuitry detects when each command is completed andgenerates the “done” signals. Essentially, there are two groups ofreasons for being “done”; normal reasons and exceptional reasons. Theseare each handled by one of the two three way multiplexers.

[1992] The lower multiplexer (i_(—)1275) handles the normal reasons. Inthe case of a FLC, the signal ndnflc is used. This is the output of thecomparator comparing the bit counter with the table number. In the caseof a VLC, the signal ndnvlc is used. This is an output from thearithmetic datapath and reflects directly Equation 9. In the case of anNOP instruction or a Token, only one cycle is required and, therefore,the system is unconditionally “done”.

[1993] In the present invention, the upper multiplexer (i_(—)1274)handles exceptional cases. If the decoder is expecting a size to be fedback (fbexpctd0) in JPEG decoding and that size is one (notfbone0), thenthe decoder is done because only one bit is required. If the decoder isdoing the Afirst bit of the first coefficient using the Tcoeff table, itis done if bit zero of the current index is zero (see SectionB.2.2.1.2). If neither of these conditions are met then there is noexceptional reason for being done.

[1994] The NOR gate (i_(—)1293) finally resolves the “done” condition.The condition generated by i-570 (i.e., that the data is not valid)forces “done”. This may seem a little strange. It is used primarily justafter reset to force the machine into its “done” state in preparationfor the first command (“done” resets all counters, registers, etc.).Note that any error condition also forces “done”.

[1995] The signal notdonex is required for use in detecting errors. Thenormal “done” signals cannot be used since on detecting an error “done”is forced anyway. The use of “done” would give a combinatorial feedbackloop.

[1996] Error detection and handling, is accomplished by circuitry whichdetects all of the possible error conditions. These are 0Red together ini_(—)1190. In this case, i_(—)1193, i-585 and i_(—)584 constitute thethree bit Huffman error register. Note i_(—)1253 and i-1254 whichdisable the error in the cases when there is no “real” error (sectionB.2.2.3).

[1997] In addition, i_(—)580 and i_(—)579 along with the associatedcircuitry provide a simple state machine that controls the acceptance ofthe first command after an error is detected.

[1998] As previously indicated, control signals are delayed to matchpipeline delays in the Index to Data Unit and the ALU.

[1999] Itod_bypass is the actual bypass signal passed to the Index toData Unit. It is modified when the Huffman State Machine is in controlto force bypass whenever a fixed length code is decoded.

[2000] Aluinstr[32] is the bit that causes the ALU to feedback(condition codes) to the Parser State Machine. Furthermore, it isimportant when the Huffman State Machine is in control that the signalsare only asserted once (rather than each time one of the primitivecommands completes).

[2001] Aluinstr[36] is the bit that allows the ALU to step the blockcounters (if other ALU instruction bits specify an increment too). Thisalso must only be asserted once.

[2002] In addition, these bits must only be asserted for ALUinstructions that output data to the Token Formatter. Otherwise, thecounters may be incremented prior to the first output to the Tokenformatter causing an incorrect value of “cc” in a DATA token.

[2003] In the illustrated embodiment of the invention, either alunode[1]or alunode[0] will be low if the ALU will output to the Token Formatter.

[2004]FIG. 118, similar to FIG. 27, illustrates the Huffman StateMachine datapath referred to as “hdstdp”. There is also a UPI decode forreading the output of the Huffman State machine ROM.

[2005] Multiplexing is provided to deal with the case when the tablenumber is specified by the ALU register file locations (see SectionB.2.2.4.6).

[2006] The modification of aluinstr[3:2] deals with forcing the ALUoutsrc instruction field to non-none (section B.2.2.5.3, description ofalueob)

[2007] Regarding the command register for the Huffman Decoder block (x),each bit of the command has associated multiplexer which selects betweenthe possible sources of commands. Four control signals control thisselection:

[2008] Selhold causes the register to retain its current state.

[2009] Selnew causes a new command to be loaded from the Parser StateMachine. This also enables loading of the registers that retain theoriginal Parser State Machine command for later use.

[2010] Selold causes loading of the command from the registers thatretain the original Parser State Machine command.

[2011] /selsm causes loading of the command from the Huffman StateMachine ROM.

[2012] In the case of the table number, the situation is slightly morecomplicated since the table number may also be loaded from the outputdata of the Index to Data Unit (selholdt and muxsize). Latches hold thecurrent address in the Huffman state machine ROM. The logic detectswhich of the possible four commands are being executed. These signalsare combined to form the lower two bits of the start address in the caseof a new command.

[2013] Logic also detects when the output of the state machine ROM ismeaningless (usually because the command is a “simple” command). Thesignal notignorerom effectively disables operation of the state machine,in particular, disabling any modification of the instruction passed tothe ALU.

[2014] The circuitry generating fixstate0 controls the limited jumpingcapability of this state machine.

[2015] Decoding is also provided for driving the signals into theHuffman State Machine ROM. This is datapath-style combinatorial ROM.

[2016] The generation of escape_run is described in Section B.2.2.5.4.

[2017] Decoding also provides for the registers that hold the HuffmanIndex number for symbols such as ZRL and EOB. D These registers can beloaded from the UPI or the datapath. The decoding in the center(es[4:0]and zs[3:0] is generating the select signals for the multiplexers thatselect which register or constant value to compare against the decodeHuffman Index.

[2018] Regarding the control logic for the Huffman State Machine. Herethe “instruction” bits from the Huffman State Machine ROM are combinedwith various conditions to determine what to do next and how to modifythe instruction word for the ALU.

[2019] In the present invention, the signals notnew, notsm and notoldare used on sheet 10 to control the operation of the Huffman Decodercommand register. They are generated here in an obvious manner from thecontrol bits in the state machine ROM (described in Section B.2.2.5.3)together with the output of the Huffman Index comparators (neobmatch andnzrlmatch).

[2020] Selection is also accomplished of the source for the instructionpassed to the ALU. The actual multiplexing is performed in the HuffmanState Machine datapath “hfstdp”. Four control signals are generated.

[2021] In the case when the end-of-block has not been encountered, oneof aluseldmx (selecting the Parser State Machine instruction) oraluselsm (selecting the Huffman state machine instruction) will begenerated.

[2022] In the case when the end-of-block has not been encountered, oneof aluseleobd (selecting the Parser State Machine instruction) oraluseleobs (selecting the Huffman State Machine instruction) will begenerated. In addition the “outsrc” field of the ALU instruction ismodified to force it to “zinput”.

[2023] A register holds the nominated table number during tabledownload. Decoding is provided for the codes-per-bit RAMs. Additionaldecoding recognizes when symbols like EOB and ZRL are downloaded so thatthe Huffman Index number registers can be automatically loaded.

[2024] Regarding the bit counter, a comparator detects when the correctnumber of bits have been read when reading a FLC.

[2025] B.2.2.6.2 Description of “hddp”

[2026] Comparators detect the specific values of Huffman Index.Registers hold the values for the downloadable tables. The multiplexers(meob[7:0] and mzr[7:0]) select which value to use and the exclusive-orgates and gating constitute the comparators.

[2027] Adders and registers directly evaluate the equations described inSection B.2.2.1. No further description is thought necessary here. Anexclusive or is used for inverting the data (i 807) described in SectionB.2.2.1.1.

[2028] The “code” register is 12 bits wide. A multiplexing arrangementimplements the “ring” substitution described in Section B.2.2.1.2.

[2029] Regarding the pipeline delays for data and multiplexing betweendecoded serial data (index[7:0]) and Token data (ntoken0[7:0]), theHuffman index value is decided in ZRL and EOB symbols.

[2030] Codes-per-bit ROMs and their multiplexing are used for decidingwhich table to use. This arrangement is used because the table selectinformation arrives late. All tables are then accessed and the correcttable selected.

[2031] Regarding the codes-per-bit RAM, the final multiplexing of thecodes-per-bit ROM and the output of the codes-per-bit RAM takes placeinside the block “hdcpbram”.

[2032] B.2.2.6.3 Description of “hdstdp”

[2033] In the present invention, “Hdstdp” comprises two modules.“hdstdel” is concerned with delaying the Parser State Machine controlbits until the appropriate pipeline stage, e.g., when they are suppliedto the ALU and Token Formatter. It only processes about half of theinstruction word that is passed to the ALU, the remainder being dealtwith by the other module “hdstmod”.

[2034] “Hdstmodt” includes the Huffman State Machine ROM. Some bits ofthis instruction are used by the Huffman State Machine control logic.The remaining bits are used to replace that part of the ALU instructionword (from the Parser State Machine) that is not dealt with in“hdstdel”.

[2035] “Hdstmod” is obvious and requires no explanation—there are onlypipeline delay registers.

[2036] “Hdstdel” is also very simple and is handled by a ROM andmultiplexers for modifying the ALU instruction. The remainder of thecircuitry is concerned with UPI read access to half of the Huffman StateMachine ROM outputs. Buffers are also used for the control signals.

[2037] B.2.3 The Token Formatter

[2038] The Huffman Decoder Token Formatter, in accordance with thepresent invention, sits at the end of the Huffman block. Its function,as its name suggests, is to format the data from the Huffman Decoderinto the propriety Token structure. The input data is multiplexed withdata in the Microinstruction word, under control of the Microinstructionword command field. The block has two operating modes; DATA_WORD, andDATA_TOKEN.

[2039] B.2.3.1 The Microinstruction Word TABLE B.2.7 TheMicroinstruction word consisting of seven fields Field Name Bits Token0:7 Mask  8:11 Block Type (Bt) 12:13 External Extn (Ee) 14 Demux Extn(De) 15 End of Block (Eb) 16 Command (Cmd) 17

[2040] The Microinstruction word is governed by the samne accept as theData word.

[2041] B.2.3.2 Operating Modes TABLE B.2.8 Bit Allocation Cmd Mode 0Data_Word 1 Data_Token

[2042] B.2.3.2.1 Data Word

[2043] In this mode, the top eight bits of the input are fed to theoutput. The bottom eight bits will be either the bottom eight bits ofthe input, the Token field of the Microinstruction word or a mixture ofboth, depending on the mask field. Mask represents the number of inputbits in the mix, i.e.

[2044] out_data[16:8.]=in_data[16:8]

[2045] out₁₃ data[7:0]=(Token[7:0]&(ff<<mask))indata[7:0]

[2046] When mask is set to 0×8 or greater, the output data will equalthe input data. This mode is used to output words in non-DATA Tokens.With mask set to 0, out_data[7:0] will be the Token field of theMicroinstruction word. This mode is used for outputting Token headersthat contain no data. When Token headers do contain data, the number ofdata bits is given by the mask field.

[2047] If External Extn(Ee) is set, out_extn=in_extn, otherwiseout_extn=De.Bt and Eb are “don't care”.

[2048] B.2.3.2.2 Data Token

[2049] This mode is used for formatting DATA Tokens and has twofunctions dependent on a signal, first coefficient. At reset, firstcoefficient is set. When the first data coefficient arrives along with aMicroinstruction word that has cmd set to 1, out_data[16:2] is set to0×1 and out_data[1:0] takes the value of the Bt field in theMicroinstruction word. This is the header of a DATA Token. When thisword has been accepted, the coefficient that accompanied the command isloaded into a register, RL and first coefficient takes the value of Eb.When the next coefficient arrives, out_data[16:0] takes the previouscoefficient, stored in RL. RL and first_coefficient are then updated.This ensures that when the end of the block is encountered and Eb isset, first_coefficient is set, ready for the next DATA Token, i.e.,If(first_coefficient) { out_data[16:2] = 0x1 out_data[1:0] = 3t[1:0]RL[16:0] = in_data[16:0] } else { out_data[16:0] = RL[16:0] RL[16:0] =in_data[16:0] } out_extn = −Eb

[2050] B.2.3.3 Explanatory Discussion

[2051] In accordance with the present invention, most of the instructionbits are supplied in the normal manner by the Parser State Machine.However, two of the fields are actually supplied by other circuitry. The“Bt” field mentioned above is connected directly to an output of the ALUblock. This two bit field gives the current value of “cc” or “colorcomponent”. Thus, when a DATA Token header is constructed, the lowestorder two bits take the color component directly from the ALU counters.Secondly, the “Eb” bit is asserted in the Huffman decoder whenever andEnd-of-block symbols id decoded (or in the case of JPEG when one isassumed because the last coefficient in the block is coded).

[2052] The in_extn signal is derived in the Huffman Decoder. It only hasmeaning with respect to Tokens when the extension bit is supplied alongwith the Token word in the normal way.

[2053] B.2.4 The Parser State Machine

[2054] The Paerser State Machine of the present invention is actually avery simple piece of circuitry. The complication lies in the programmingof the microcode ROM which is discussed in Section B.2.5.

[2055] Essentially the machine consists of a register which holds thecurrent address. This address is looked up in the microcode ROM toproduce the microcode word. The address is also incremented in a simpleincrementer and this incremented address is one of two possibleaddresses to be used for the next state. The other address is a field inthe microcode ROM itself. Thus, each instruction is potentially a jumpinstruction and may jump to a location specified in the program. If thejump is not taken, control passes to the next location in the ROM.

[2056] A series sixteen condition code bits are provided. Any one ofthese conditions may be selected (by a field in the microcode ROM) and,in addition, it may be inverted (again a bit in the microcode ROM). Theresulting signal selects between either the incremented address or thejump address in the microcode ROM. One of the conditions is hard-wiredto evaluate as “False”. If this condition is selected, no jump willoccur. Alternatively, if this condition is selected and then inverted,the jump is always taken; an unconditional jump. TABLE B.2.9 ConditionCode Bits Bit No. Name Description 0 user[0] Connected to a registerprogrammable by 1 user[1] the user from the microprocessor interface.They 2 cbp_eight allow ‘user defined’ condition codes that 3 cbp_specialcan be tested with little overhead. Two are defined to controlnon-standard ‘Coded block Pattern’ processing for experimental 4 blockand 8 block macroblock structures. 4 he[0] These bits connect directlyto the Huffman 5 he[1] decoder's Huffman Error register. 6 he[2] 7 ExtnThe Extension bit (for Tokens) 8 Blkptn The Block Pattern Shifter 9MBstart At Start of Macroblock 10 Picstart At Start of a Picture 11Restart At Start of a Restart interval 12 Chngdet The ‘Sticky’ ChangeDetect bit 13 Zero ALU zero condition 14 Sign ALU sign condition 15False Hard wired to False.

[2057] B.2.4.1 Two Wire Interface Control

[2058] The two-wire interface control, in accordance with the invention,is a little unusual in this block. There is a two-wire interface betweenthe Parser State Machine and the Huffman Decoder. This is used tocontrol the progress of commands. The Parser State Machine will waituntil a given command has been accepted before it proceeds to read thenext command from the ROM. In addition, condition codes are fed backthrough a wire from the ALU.

[2059] Each command has a bit in the microcode ROM that allows it tospecify that it should wait for feedback. If this occurs, then afterthat instruction has been accepted by the Huffman Decoder, no newcommands are presented until the feedback wire from the ALU becomesasserted. This wire, fb_valid, indicates that the condition codescurrently being supplied by the ALU are valid in the sense that theyreflect the data associated with the command that requested the wait forfeedback.

[2060] The intended use of the feature, in accordance with the presentinvention, is in constructing conditional jump commands that decide thenext state to jump to as a result of decoding (or processing) aparticular piece of data. Without this facility it would be impossibleto test any conditions depending upon data in the pipeline since thetwo-wire control means that the time at which a certain command reachesa given processing block (i.e., the ALU in this case) is uncertain.

[2061] Not all instructions are passed to the Huffman Decoder. Someinstructions may be executed without the need for the data pipeline.These tend to be jump instructions. A bit in the microcode ROM selectswhether or not the instruction will be presented to the Huffman Decoder.If not, there is no requirement that the Huffman Decoder accept theinstruction and, therefore, execution can continue in thesecircumstances even if the pipeline is stalled.

[2062] B.2.4.2 Event Handling

[2063] There are two event bits located in the Parser State Machine. Oneis referred to as the Huffman event and the other is referred to as theParser Event.

[2064] The Parser Event is the simplest of these. The “condition” beingmonitored by this event is simply a bit in the microcode ROM. Thus, aninstruction may cause a Parser Event by setting this bit. Typically, theinstruction that does this will write an appropriate constant into therom_control register so that the interrupt service routine can determinethe cause of the interrupt.

[2065] After servicing a Parser Event (or immediately if the event ismasked out) control resumes at the point where it left off. If theinstruction that caused the event has a jump instruction (whosecondition evaluates true) then the jump is taken in the normal manner.Hence, it is possible to jump to an error handler after servicing bycoding the jump.

[2066] A Huffman event is rather different. The condition beingmonitored is the “OR” of the three Huffman Error bits. In reality, thiscondition is handled in a very similar manner to the Parser Event.However, an additional wire from the Huffman Decoder, huffintrpt, isasserted whenever an error occurs. This causes control to jump to anerror handler in the microcode program.

[2067] When a Huffman error occurs, therefore, the sequence involvesgenerating interrupt and stopping the block. After servicing, control istransferred to the error handler. There is no “call” mechanism andunlike a normal interrupt, it is not possible to return to the point inthe microcode before the error occurred following error handling.

[2068] It is possible for huffintrpt to be asserted without a Huffmanerror being generated. This occurs in the special case of a “no-error”error as discussed in Section B.2.2.3. In this case, no interrupt (tothe microprocessor interface) is generated, but control is still passedto the error handler (in the microcode). Since the Huffman errorregister will be clear in this case, the microcode error handler candetermine that this is the situation and respond accordingly.

[2069] B.2.4.3 Special Locations

[2070] There are several special locations in the microcode ROM. Thefirst four locations in the ROM are entry points to the main program.Control passes to one of these four locations on reset. The locationjumped to depends upon the coding standard selected in the ALU register,coding_std. Since this location is itself reset to zero by a true resetcontrol passes to location zero. However, it is possible to reset theParser State Machine alone by using the UPI register bit CED_H_TRACE_RSTin CED_H_TRACE. In this case, the coding_std register is not reset andcontrol passes to the appropriate one of the first four locations.

[2071] The second four locations (0×004 to 0×007) are used when aHuffman interrupt takes place. Typically, a jump to the actual errorhandler is placed in each of these locations. Again, the choice oflocation is made as a result of the coding standard.

[2072] B.2.4.4 Tracing

[2073] As a diagnostic aid, a trace mechanism is implemented. Thisallows the microcode to be single-stepped. The bits CED_H_TRACE_EVENTand CED_H_TRACE_MASK in the register CED_H_TRACE control this. As theirnames suggest, they operate in a very similar fashion to the normalevent bits. However, because of several differences (in particular noUPI interrupt is ever generated) they are not grouped with the otherevent bits.

[2074] The tracing mechanism is turned on when CED_H_TRACE_MASK is setto one. After each microcode instruction is read from the ROM, butbefore it is presented to the Huffman Decoder, a trace event occurs. Inthis case, CED_H_TRACE_EVENT becomes one. It must be polled because nointerrupt will be generated. The entire microcode word is available inthe registers CED_H_KEY_DMX_WORD_(—)0 through CED_H_KEY_DMX₌₁₃WORD_(—)9. The instruction can be modified at this time if required.Writing a one to CED_H_TRACE_EVENT causes the instruction to be executedand clears CED_H_TRACE_EVENT. Shortly after this time, when the nextmicrocode word to be executed has been read from the ROM, a new traceevent will occur.

[2075] B.2.5 The Microcode

[2076] The microcode is programmed using an assembler “hpp” which is avery simple tool and much of the abstraction is achieved by using amacro preprocessor. A standard “C” preprocessor “cpp” may be used forthis purpose.

[2077] The code is instructed as follows:

[2078] Ucode.u is the main file. First, this includes tokens.h to definethe tokens. Next, regfile.h defines the ALU register map. The fields.udefines the various fields in the microcode word, giving a list ofdefined symbols for each possible bit pattern in the field. Next, thelabels that are used in the code are defined. After this step, instr.uis included to define a large number of “cpp” macros which define thebasic instructions. Then, errors.h defines the numbers which define theParser events. Next, unword.u defines the order in which the fields areplaced to build the microcode word.

[2079] The remainder of ucode.u is the microcode program itself.

[2080] B.2.5.1 The Instructions

[2081] In this section the various instructions defined in ucode.u aredescribed. Not all instructions are described here since in many casesthey are small variations on a theme (particularly the ALUinstructions).

[2082] B.2.5.1.1 Huffman and Index to Data Instructions

[2083] In the invention, the H_NOP instruction is used by the HuffmanDecoder. It is the No-operation instruction. The Huffman does nothing inthe sense that no data is decoded. The data produced by this instructionis always zero. Accordingly, the associated instruction is passed ontothe ALU.

[2084] The next instructions are the Token groups; H_TOKSRCH,H_TOKSKIP_PAD, H_TOKSKIP_JPAD, H_TOKPASS and H_TOKREAD. These all read atoken or tokens from the Input Shifter and pass them onto the rest ofthe machine. H_TOKREAD reads a single token word. H_TOKPASS can be usedto read an entire token, up to and including, the word with a zero extnbit. The associated command is repeated for each word of the Token.H_TOKSRCH discards all serial data preceding a Token and then reads onetoken word. H_TOKSKIP_PAD skips any padding bits (H.261 and MPEG) andthen reads one Token word. H_TOKSKIPJ_PAD does the same thing for JPEGpadding.

[2085] H_FLC(NB) reads a fixed length code of “NB” bits.

[2086] H_VLC(TBL) reads a vic using the indicated table (passed asmnemonic, e.g., H_VLC(tcoeff)).

[2087] H_FLC_IE(NB) is like H_FLC, but the “ignore errors” bit is set.

[2088] H_TEST_VLC(TBL) is like H_VLC, but the bypass bit is set so thatthe Huffman Index is passed through the Index to Data Unit unmodified.

[2089] H_FWD_R and H_BWD_R read a FLC of the size indicated by the ALUregisters r_fwd_r_size and r_bwd_r_size, respectively.

[2090] H_DCJ reads JPEG style DC coefficients, the table number from theALU.

[2091] H_DCH reads a H.261 DC term.

[2092] H_TCOEFF and H_DCTCOEFF read transform coefficients. InH_DCTCOEFF, the first coeff bit is set and is for non-intra blocks,whilst H_TCOEFF is for intra blocks after the DC term has already beenread.

[2093] H_NOMINATE(TBL) nominates a table for subsequent download.

[2094] H_DNL(NB) reads NB bits and downloads them into the nominatedtable.

[2095] B.2.5.1.2 ALU Instructions

[2096] There really are too many ALU instructions to explain them all indetail. The basic way in which the Mnemonics are constructed isdiscussed and this should make the instructions readable. Furthermore,these should readily be understandable to one of ordinary skill in theart.

[2097] Most of the ALU instructions are concerned with moving data fromplace to place and, therefore, a generic “load” instruction is used. Inthe Mnemonic, A_LDxy, it is understood that the contents of y are loadedinto x., i.e., the destination is listed first and the source second:TABLE B.2.10 Letters used to denote possible sources and destinations ofdata Letter Meaning A A register R Run register I Data Input O DataOutput F ALU register File C Constant Z Constant of zero

[2098] By way of example, LDAI loads the A register with the data fromthe data input port of the ALU. If the ALU register file is specified,the mnemonic will take an address so that LDAF(RA) loads A with thecontents of location RA in the register file.

[2099] The ALU has the ability to modify data as it is moved from sourceto destination. In this case, the arithmetic is indicated as part of thesource data. Accordingly, the Mnemonic LDA_AADDF(RA) loads A with theexisting contents of the A register plus the contents of the indicatedlocation in the register file. Another example is LDA_ISGXR, which takesthe input data, sign extends from the bit indicated in the RUN register,and stores the result in the A register.

[2100] In many cases, more than one destination for the same result isspecified. Again, by way of example, LDF_LDA_ASUBC(RA) which loads theresult of A minus a constant into both the A register and the registerfile.

[2101] Other mnemonics exist for specific actions. For example, “CLRA”is used for clearing the A register, “RMBC” to reset the macroblockcounter. These are fairly obvious and are described in comments ininstr.u.

[2102] One anomaly is the use of a suffix “_O” to indicate that theresult of the operation is output to the Token formatter in addition tothe normal action. Thus LDFI_O(RA) stores the input data and also passesit to the token formatter. Alternatively, this could have beenLDF_LDO_I(RA) if desired.

[2103] B.2.5.1.3 Token Formatter Instructions

[2104] This is the T_NOP “No-operation” instruction. This is really amisnomer as it is impossible to construct a no-operation instruction.However, this is used whenever the instruction is of no consequencebecause the ALU does not output to the Token Formatter.

[2105] T-TOK output a Token word.

[2106] T_DAT output a DATA Token word (used only with the Huffman StateMachine instructions).

[2107] T-GENT8 generates a token word based on the 8 bits of constantfield.

[2108] T_GENT8E like T_GENT8, but the extension bit is one.

[2109] T_OPD(NB) NB bits of data from the bottom NB bits of the outputwith the remainder of the bits coming from the constant field.

[2110] T_OPDE(NB) like T_OPD, but the extension bit is high.

[2111] T_OPD8 short-hand for T_OPD(8)

[2112] T_OPD8E short-hand for T_OPDE(8)

[2113] B.2.5.1.4 Parser State Machine Instructions

[2114] This instruction, D_NOP No-operation, i.e., the addressincrements as normal and the Parser State Machine does nothing special.The Remainder of the instruction is passed to the data pipeline. Nowaiting occurs.

[2115] D_WAIT is like D_NOP, but waits for feedback to occur.

[2116] The simple jump group. Mnemonics like D_JMP(ADDR) and D_JNX(ADDR)jump if the condition is met. The instruction is not output to theHuffman Decoder.

[2117] The external jump group. Mnemonics like D_XJMP(ADDR) andD_XJNX(ADDR). These are like their simple counterparts above, but theinstruction is output to the Huffman Decoder.

[2118] The jump and wait group. Mnemonics like D_WJNZ(ADDR). Theseinstructions are output to the Huffman Decoder and the Parser waits forfeedback from the ALU before evaluating the condition.

[2119] The following Mnemonics are used for the conditions themselves.TABLE B.2.11 Mnemonics used for the conditions Mnemonic Meaning JMP —Unconditional jump JXT JNX Jump if extn=1 (extn=0) JHE0 JNHE0 Jump ifHuffman error bit 0 set (clear) JHE1 JNHE1 Jump if Huffman error bit 1set (clear) JHE2 JNHE2 Jump if Huffman error bit 2 set (clear) JPTN —Jump if pattern shifter LSB is set JPICST JNPICST Jump is at picturestart (not at picture start) JRSTST JNRSTST Jump if at start of restartinterval (not at start) . JNCPBS Jump if not special CPB coding . JNCPB8Jump if not 8 block (i.e. 4 block) macroblock JMI JPL Jump if negative(jump if plus) JZE JNZ Jump if zero (jump if non-zero) JCHNG JNCHNG Jumpif change detect bit set (clear) JMBST JNMBST Jump if at start ofmacroblock (not at start)

[2120] D_EVENT causes generation of an event.

[2121] D_DFLT for construction of a default instruction. This causes anevent and then jumps to a location with the label “dflt” Thisinstruction should never be executed since they are used to fill a ROMso that a jump to an unused location is trapped.

[2122] D_ERROR causes an event and then jumps to a label “srch_dispatch”which is assumed to attempt recovery from the error.

[2123] SECTION B.3 HUFF DECODER ALU

[2124] B.3.1 Introduction

[2125] The Huffman Decoder ALU sub-block, in accordance with the presentinvention, provides general arithmetic and logical functionality for theHuffman Decoder block. It has the ability to do add and subtractoperations, various types of sign-extend operations, and formatting ofthe input data into run-sign-level triples. It also has a flexiblestructure whose precise operation and configuration are specified by amicroinstruction word which arrives at the ALU synchronously with theinput data, i.e., under the control of the two-wire interface.

[2126] In addition to the 36-bit instruction and 12-bit data inputports, the ALU has a 6-bit run port, and an 8-bit constant port (whichactually resides on the token bus). All of these, with the exception ofthe microinstruction word, drive buses of their respective widthsthrough the ALU datapath. There is a single bit within themicroinstruction word which represents an extension bit and is outputtogether with the 17-bit-run-sign-level (out_data). There is a two-wireinterface at each end of the ALU datapath, and a set of condition codeswhich are output together with their own valid signal, cc_valid. Thereis a register file which is accessible to other Huffman Decodersub-blocks via the ALU, and also to the microprocessor interface.

[2127] B.3.2.2 Basic Structure

[2128] The basic structure of the Huffman ALU is as shown in FIG. 126.It comprises the following components:

[2129] Input block 400

[2130] Output block 401

[2131] Condition Codes block 402

[2132] “A” register 403 with source multiplexing

[2133] Run register (6 bits) 404 with source multiplexing

[2134] Adder/Subtractor 405 with source multiplexing

[2135] Sign Extend logic 406 with source multiplexing

[2136] Register file 407

[2137] Each of these blocks (except the output block) drives its outputonto a bus running through the datapath, and these buses are, in turn,used as inputs to the multiplexing for block sources. For example, theadder output has it own datapath bus which is one of the possible inputsto the A register. Likewise, the A register has its own bus which formsone of the possible inputs to the adder. Only a sub-set of allpossibilities exist in this respect, as specified in Section 7 on themicroinstruction word.

[2138] In a single cycle, it is possible to execute either an add-basedinstruction or a sign-extend-based instruction. Furthermore, it isallowable to execute both of these in a single cycle provided that theiroperation is strictly parallel. In other words, add then sign extend orsign extend then add sequences are not allowed. The register file may beeither read from or written to in a single cycle, but not both.

[2139] The output data has three fields:

[2140] run—6 bits

[2141] sign—1 bit

[2142] level—10 bits

[2143] If data is to be passed straight through the ALU, the leastsignificant 11 bits of the input data register are latched into the signand level fields.

[2144] It is possible to program limited multi-cycle operations of theALU. In this regard, the number of cycles required is given by thecontents of the register file location whose address is specified in themicroinstruction, and the same operation is performed repeatedly whilean iteration counter decrements to one. This facility is typically usedto effect left shifts, using the adder to add the A register to itselfand to store the result back in the A register.

[2145] B.3.3 The Adder/Subtractor Sub-Block

[2146] This is a 12-bit wide adder, with optional invert on its input2and optional setting of the carry-in bit. Output is a 12 bit sum, andcarry-out is not used. There are 7 modes of operation:

[2147] ADD: add with carry in set to zero: input1+input2

[2148] ADC: add with carry in set to one: input1+input2+1

[2149] SBC: invert input2, carry in set to zero: input1−input2−1

[2150] SUB: invert input2, carry in set to one: input1−input2

[2151] TCI: if input2<0, use SUB, else use ADD. This is used with inputlset to zero for obtaining a magnitude value from a two's complimentvalue.

[2152] DCD (DC difference): if input2<0 do ADC, otherwise do ADD.

[2153] VRA (vector residual add): if input1<0 do ADC, otherwise do SBC.

[2154] B.3.4 The Sign Extend Sub-Block

[2155] This is a 12-bit unit which sign extends, in various modes, theinput data from the size input. Size is a 4 bit value ranging from 0 to11 (0 relates to the least significant bit, 11 to the most significant).Output is a 12 bit modified data value, and the “sign” bit.

[2156] In SGXNODE=NORMAL, all bits above (and including) the size-thbit, take the value of the size-th bit. All those below remainunchanged. Sign takes the value of the size-th bit. For example:

[2157] data=1010 1010 1010

[2158] size=2

[2159] output=0000 0000 0010, sign=0

[2160] In SGXMOD=INVERSE, all bits above (and including) the size-thbit, take the inverse of the size-th bit, while all those below remainunchanged. Sign takes the inverse of the size-th bit. For example:

[2161] data=1010 1010 1010

[2162] size=0

[2163] output=1111 1111 1111, sign=1

[2164] In SGXMODE=DIFMAG, if the size-th bit is zero, all the bits below(and including) the size-th bit are inverted, while all those aboveremain unchanged. If the size-th bit is one, all bits remain unchanged.In both cases, sign takes the inverse of the size-th bit. This is usedfor obtaining the magnitude of AC difference values. For example:

[2165] data=0000 1010 1010

[2166] size=2

[2167] output=0000 1010 1101, sign=1

[2168] data=0000 1010 1010

[2169] size=1

[2170] output=0000 1010 1010, sign=0

[2171] In SGXMODE=DIFCOMP, all bits above (but not including) thesize-th bit, take the inverse of the size-th bit, while all those below(and including) remain unchanged. Sign takes the inverse of the size-thbit. This is used for obtaining two's compliment values for DCdifference values. For example:

[2172] data=1010 1010 1010

[2173] size=0

[2174] output=1111 1111 1110, sign=1

[2175] B.3.5 Condition Codes

[2176] There are two bytes (16 bits) of condition codes used by theHuffman block, certain bits of which are generated by the ALU/registerfile. These are the Sign condition code, the Zero condition code, theExtension condition code and a Change Detect bit. The last two of thesecodes are not really condition codes since they are not used by theParser in the same way as the others.

[2177] The Sign, Zero and Extension condition codes are updated when theParser issues an instruction to do so, and for each of theseinstructions the condition code valid signal is pulsed high once.

[2178] The Sign condition code is simply the sign extend sign outputlatched, while the Zero condition code is set to 1 if the input to the Aregister is zero. The Extension condition code is the input extensionbit latched regardless of OUTSRC.

[2179] Condition codes may be used to evaluate certain condition types:

[2180] result equals constant—use subtract and Zero condition

[2181] result equals register value—use subtract and Zero condition

[2182] register equals constant—use subtract and Zero condition.

[2183] register bit set—use sign extend and Sign condition

[2184] result bit set—use sign extend and Sign condition

[2185] Note that when using the sign extend and Sign condition codecombination, it is possible only to evaluate a single specified bit,rather than multiple bits as would be the case with a conventionallogical AND.

[2186] The Change Detect bit, in the present invention, is generatedusing the same logic as for the Zero condition code, but it does nothave an associated valid signal. A bit in the microinstruction indicatesthat the Change Detect bit should be updated if the value currentlybeing written to the register file is different from that alreadypresent (meaning that two clock cycles are necessary, first withREG-MODE set to READ and second with REGMODE set to WRITE). Amicroprocessor interrupt can then be initiated if a changed value isdetected. The Change Detect bit is reset by activating Change Detect inthe normal way, but with REGMODE set to READ.

[2187] The hardwired macroblock counter structure (which forms part ofthe register file—see below) also generates condition codes as follows:Mb_Start, Pattern_Code, Restart and Pic_Start.

[2188] B.3.6 The Register File

[2189] The address map for the register file is shown below. It uses a7-bit address space, which is common to both the ALU datapath and theUPI. A number of locations are not accessed by the ALU, these typicallybeing counters in the hardwired macroblock structure, and registerswithin the ALU itself. The latter have dedicated access, but form partof the address map for the UPI. Some multi-byte locations (denoted inthe table by “O” for oversize) have a single ALU address, but multipleUPI addresses. Similarly, groups of registers which are indexed by thecomponent count, CC (Indicated by I″ in the table) are treated as asingle location by the ALU. This eases microprogramming forinitialization and resetting, and also for block-level operations.

[2190] All of the locations, except the dedicated ALU registers (UPIread only), are read/write, and all of the counters are reset to zero bya bit in the instruction word. The pattern code register has a rightshift capability, its least significant bit forming the Pattern Codecondition bit. All registers in the hardwired macroblock structure aredenoted in the table by “M”, and those which are also counters (n-bit)are annotated with Cn.

[2191] In the present invention, certain locations have their contentshardwired to other parts of the Huffman sub-system-coding standard, twor-size locations, and a single location (2-bit word) for each of ac hufftable and dc huff table to the Huffman Decoder.

[2192] Addresses in bold indicate that locations are accessible by boththe ALU and the UPI, otherwise they have UPI access only. Groups ofregisters that are undirected through CC by the ALU can have a singleALU address specified in the instruction word and CC will select whichphysical location in the group to access. The ALU address may be that ofany of the registers in the group, though conventionally, the address ofthe first should be used. This is also the case for multi-byte locationswhich should be accessed using the lowest address of the pair, althoughin practice, either address will suffice. Note that locations 2E and 2Fare accessible in the top-level address map (denoted “T”), i.e., notonly through the keyhole registers. These two locations are also resetto zero.

[2193] The register file is physically partitioned into four “banks” toimprove access speed, but this does not affect the addressing in anyway. The main table shows allocations for MPEG, and the too repeatedsections give the variations for JPEG and H.261 respectively. TABLEB.3.1 Table 1: Huffman Register File Address Map Addr Location 00 Aregister 1 01 A register 0 02 run 10 horiz pels 1 11 horiz pels 0 12vert pels 1 13 vert pels 0 14 buff size 1 15 buff size 0 16 pel asp.ratio 17 bit rate 2 18 bit rate 1 19 bit rate 0 1A pic rate 1Bconstrained 1C picture type 1D H261 picture type 1E broken closed 1Fpred mode 20 vbv delay 1 21 vbv delay 0 22 full pel fwd 23 full pel bwd24 horiz mb copy 25 pic number 26 max h 27 max v 28 — 29 — 2A — 2B — 2Cfirst group 2D in picture T.R 2E rom control T.R 2F rom revision I.H 30dc huff 0 I 31 dc huff 1 I 32 dc huff 2 I 33 dc huff 3 I.H 34 ac huff 0I 35 ac huff 1 I 36 ac huff 2 I 37 ac huff 3 I 38 tq0 I 39 tq1 I 3A tq2I 3B tq3 I 3C c0 I 3D c1 I 3E c2 I 3F c3 I.O 40 cc pred_01 I.O 41 ccpred_00 I.O 42 cc pred_01 I.O 43 dc pred_10 I.O 44 dc pred_21 I.O 45 dcpred_20 I.O 46 dc pred_31 I.O 47 dc pred_3 0 O 50 prev mhf 1 O 51 prevmhf 0 O 52 prev mvf 1 O 53 prev mvf 0 O 54 prev mhb 1 O 55 prev mhb 0 O56 prev mvb 1 O 57 prev mvb 0 M 60 mb horiz cnt1 C13 M 61 mb horiz cnt0— M 62 mb vert cnt1 C13 M 63 mb vert cnt0 — M 64 horiz mb 1 M 65 horizmb 0 M 66 vert mb 1 M 67 vert mb 0 M 68 restart count1 C16 M 69 restartcount0 — M 6A restart gap1 M 6B restart gap0 M 6C horiz blk count C2 M6D vert blk count C2 H.M 6E comp id C2 M 6F max comp id H.R 70 codingstd M.H 71 pattern code SR8 H 72 fwd r size H 73 bwd r size M.I 78 h0M.I 79 h1 M.I 7A h2 M.I 7B h3 M.I 7C v0 M.I 7D v1 M.I 7E v2 M.I 7F v3

[2194] TABLE B.3.2 JPEG Variations: 10 horiz pels 1 11 horiz pels 0 12vert pels 1 13 vert pels 0 14 buff size 1 15 buff size 0 16 pel asp.ratio 17 bit rate 2 18 bit rate 1 19 bit rate 0 1A pic rate 1Bconstrained 1C picture type 1D H261 picture type 1E broken closed 1Fpred mode 20 vbv delay 1 21 vbv delay 0 22 pending frame ch 23 restartindex 24 horiz mb copy 25 pic number 26 max h 27 max v 28 — 29 — 2A — 2B— 2C first scan 2D in picture 2E rom control 2F rom revision

[2195] TABLE B.3.3 H.261 Variations 10 horiz pels 1 11 horiz pels 0 12vert pels 1 13 vert pels 0 14 buff size 1 15 buff size 0 16 pel asp.ratio 17 bit rate 2 18 bit rate 1 19 bit rate 0 1A pic rate 1Bconstrained 1C picture type 1D H261 picture type 1E broken closed 1Fpred mode 20 vbv delay 1 21 vbv delay 0 22 full pel fwd 23 full pel bwd24 horiz mb copy 25 pic number 26 max h 27 max v 28 — 29 — 2A — 2B ingob 2C first group 2D in picture 2E rom control 2F rom revision

[2196] B.3.7 The Microinstruction Word

[2197] The ALU microinstruction word, in accordance with the presentinvention, is split into a number of fields, each controlling adifferent aspect of the structure described above. The total number ofbits used in the instruction word is 36, (plus 1 for the extension bitinput) and a minimum of encoding across fields has been adopted so thatnmaximum flexibility of hardware configuration is maintained. Theinstruction word is partitioned as detailed below. The default fieldvalues, that is, those which do not alter the state of the ALU orregister file, are those given in the italics. TABLE B.3.4 Table 2:Huffman ALU microinstruction fields Field Value Description Bits OUTSRCRSA6 run, sign, A register as 6 bits 0000 (specifies ZZA zero, zero, Aregister 0001 sources for ZZA8 zero, zero, A register is 8 bits 0010run, sign and ZZADDU4 zero, zero, adder o/p ms 4 bits 0011 level output)ZINPUT zero, input data 0100 RSSGX run, sign, sign extend o/p 0111 RSADDrun, sign, adder o/p 1000 RZADD run, zero, adder o/p 1001 RIZADD inputrun, zero, adder output ZSADD zero, sign, adder o/p 1010 ZZADD zero,zero, adder o/p 1011 NONE no valid output - out_valid set to zero 11XXREGADDR 00-7F register file address for ALU access 7 bits REGSRC ADDdrive adder o/p onto register file i/p 0 SGX drive sign extend o/p ontoregister file i/p 1 REGMODE READ read from register file 0 WRITE writeto register file 1 CNGDET TEST update change detect if REGMODE is 0WRITE (change HOLD do not update change detect bit 1 detect) CLEAR resetchange detect if REGMODE is READ 0 RUNSRC RUNIN drive run i/p onto runregister i/p 0 (run source) ADD drive adder o/p onto run register i/p 1RUNMODE LOAD update run register 0 HOLD do not update run register 1ASRC ADD drive adder o/p onto A register i/p 00 (A register INPUT driveinput data onto A register i/p 01 source) SGX drive sign extend o/p ontoA register i/p 10 REG drive register file o/p onto A register i/p 11AMODE LOAD update A register 0 HOLD do not update A register 1 SGXMODENORMAL sign extend with sign 00 (sign extend INVERSE sign extend with -sign 01 mode - see DIFMAG invert lower bits if sign bit is 0 10 section4) DIFCOMP sign extend with - sign from next bit up 11 SIZESRC CONSTdrive const. i/p onto sign extend size i/p 00 (source for A drive Aregister onto sign extend size i/p 01 sign extend REG drive reg.file o/ponto sign extend size i/p 10 size input) RUN drive run reg. onto signextend size i/p 11 SGXSRC INPUT drive input data onto sign extend datai/p 0 (sgx input) A drive A register onto sign extend data i/p 1 ADDMODEADD input1 + input2 000 (adder mode ADC input1 + input2 + 1 001 seesect. 3) SBC input1 − input2 − 1 010 SUB input1 − input2 011 TCI SUB ifinput2<0, else ADD - 2's comp. 100 DCD ADC if input2<0, else ADD - DCdiff 101 VRA ADC if input1<0, else SBC-vec resid add 110 ADDSRC1 A driveA register onto adder input1 00 (source for REG drive register file o/ponto adder i/p 1 01 adder i/p 1 - INPUT drive input data onto adderinput1 10 non-invert) ZERO drive zero onto adder input1 11 ADDSRC2 CONSTdrive constant i/p onto adder input2 00 (source for A drive A registeronto adder input2 01 inverting INPUT drive input data onto adder input210 input) REG drive register file o/p onto adder i/p2 11 CNDC- TESTupdate condition codes 0 MODE (cond. codes) HOLD do not update conditioncodes 1 CNTMODE NOCOUNT do not increment counters X00 (mbstructureBCINCR increment block counter and ripple 001 count mode) CCINCR forcethe component count to incr 010 RESET reset all counters in mb structure011 DISABLE disable all counters 1XX INSTMODE MULTI iterate currentinstr multi times 0 SINGLE single cycle instruction only 1

[2198] SECTION B.4 Buffer Manager

[2199] B.14e Introduction

[2200] This document describes the purpose, actions and implementationof the Buffer Manager, in accordance with the present invention (bmen).

[2201] B.4.2 Overview

[2202] The buffer manager provides four addresses for the DRAMinterface. These addresses are page addresses in the DRAM. The DRAMinterface maintains two FIFOs in the DRAM, the Coded Data Buffer and theToken Data Buffer. Hence, for the four addresses, there is a read and awrite address for each buffer.

[2203] B.4.3 Interfaces

[2204] The Buffer Manager is connected only to the DRAM interface and tothe microprocessor. The microprocessor need only be used for setting upthe “Initialization registers” shown in Table B.4.4. The interface withthe DRAM interface is the four eighteen bit addresses controlled by aREQuest/ACKnowledge protocol for each address. (Since the Buffer Manageris not in the datapath, the Buffer Manager lacks a two-wire interface.)

[2205] Furthermore, the Buffer Manager operates off the DRAM interfaceclock generator and on the DRAM interface scan chain.

[2206] B.4.4 Address Calculation

[2207] The read and write addresses for each buffer are generated from 9eighteen bit registers:

[2208] Initialization registers (RW from microprocessor)

[2209] BASECB—base address of coded data buffer

[2210] LENGTHCB—maximum size (in pages of coded data buffer

[2211] BASETB—base address of token data buffer

[2212] LENGTHTB—maximum size (in pages) of token data buffer

[2213] LIMIT—size (in pages) of the DRAM.

[2214] Dynamic registers (RO from microprocessor)

[2215] READCB—coded data buffer read pointer relative to BASECB

[2216] MMERCB—coded data buffer write pointer relative to READCB

[2217] READTB—token data buffer read pointer relative to BASETB

[2218] NUMBERTB—token data buffer write pointer relative to READTB

[2219] To calculate addresses:

[2220] readaddr=(BASE+READ) mod LIMIT

[2221] writeaddr=(((READ+NUPMBER) mod LENGTH)+BASE) mod LIMIT

[2222] The “mod LIMIT” term is used because a buffer may wrap aroundDRAM.

[2223] B.4.5 Block Description

[2224] In the present invention, and as shown in FIG. 127, the BufferManager is composed of three top level modules connected in a ring whichsnooper monitors the DRAM interface connection. The modules are bmprtize(prioritize), bminstr (instruction), and bmrecalc (recalculate) arearranged in a ring of that order and omsnoop (snoopers) is arranged onthe address outputs. The module, Bmprtize, deals with the REQ/ACKprotocol, the FULL/EMPTY flags for the buffers and it maintains thestate of each address, i.e., “is it a valid address?”. From thisinformation, it dictates to bminstr which (if any) address should berecalculated. It also operates the BUF_CSR (status) microprocessorregister, showing FULL/EMPTY flags, and the buf_access microprocessorregister, controlling microprocessor write access to the buffer managerregisters.

[2225] The module, Bminstr, on being told by bmprtize to calculate anaddress, issues six instructions (one every two cycles) to controlbmrecalc to calculating an address.

[2226] The module, Bmrecalc, recalculates the addresses under theinstruction of bminstr. Running an instruction every two cycles, itcontains all of the initialization and dynamic registers, and a simpleALU capable of addition, subtraction and modulus. It informs Sbmprtizeof FULL/EMPTY states it detects and when it has finished calculating anaddress.

[2227] B.4.6 Block Implementation

[2228] B.4.6.1 Bmprtize

[2229] At reset, the buf_access microprocessor register is set to one toallow the setting up of the initialization registers. While buf_accessreads back one, no address calculations are initiated because they aremeaningless without valid initialization registers.

[2230] Once buf_access is de-asserted (write zero to it) bmprtize goesabout making all the addresses valid (by recalculating them) since itspurpose is to keep all four addresses valid. At this stage, the BufferManager is “starting up” (i.e., all addresses have not yet beencalculated), thus, no requests are asserted. Once all addresses havebecome valid start-up ends and all requests are asserted. From thispoint forward, when an address becomes invalid (because it has been usedand acknowledged) it will be recalculated.

[2231] No prioritizing between addresses will ever need to be performed,because the DRAM interface can, at its fastest, use an address everyseventeen cycles, while the Buffer Manager can recalculate an addressevery twelve cycles. Therefore, only one address will ever be invalid atone time after start-up. Accordingly, bmprtize will recalculate anyinvalid address that is not currently being calculated.

[2232] In the invention, start-up will be re-entered whenever buf_accessis asserted and, therefore, no addresses will be supplied to the DRAMinterface during microprocessor accesses.

[2233] B.4.6.2 Bminstr

[2234] The module, Bminstr, contains a MOD 12 cycle counter (the numberof cycle it takes to generate an address). Note that even cycles startan instruction, whereas odd cycles end an instruction. The top 3 bitsalong with whether it is a read or a write calculation are decoded into,instructions for bmrecalc as follows:

[2235] For read addresses: TABLE B.4.1 Read address calculation Oper-Meaning of Cycle ation BusA BusB Result result's sign 0-1 ADD READ BASE2-3 MOD Accum LIMIT Address 4-5 ADD READ “1” 6-7 MOD Accum LENGTH READ8-9 SUB NUMBER “1” NUMBER 10-11 MOD “0” Accum SET_EMPTY (NUMBER >= 0)

[2236] For write addresses: TABLE B.4:2 For write address calculationsMeaning of Cycle Operation BusA BusB Result result's sign 0-1 ADD NUMBERREAD 2-3 MOD Accum LIMIT 4-5 ADD Accum BASE 6-7 MOD Accum LIMIT Address8-9 ADD NUMBER “1” NUMBER 10-11 MOD Accum LENGTH SET_FULL (NUMBER >=LENGTH)

[2237] Note: The result of the last operation is always held in theaccumulator.

[2238] When there is no addresses to be recalculated, the cycle counteridles at zero, thus causing an instruction that writes to none of theregisters. This has no affect.

[2239] B.4.6.3 Bmrecalc

[2240] The module, Bmrecalc, performs one operation every two clockcycles. It latches in the instruction from bminstr (and which buffer andio type) on an even counter cycle (start_alu_cyc), and latches theresult of the operation on an odd counter cycle (end_alu_cyc). Theresult of the operation is always stored in the “Accum” register inaddition to any registers specified by the instruction. Also, onend_alu_cyc, bmrecalc informs bmprtize as to whether the use of theaddress just calculated will make the buffer full or empty, and when theaddress and full/empty has been successfully calculated (load_addr).

[2241] Full/empty are calculated using the sign bit of the operation'sresult.

[2242] The modulus operation is not a true modulus, but A mod B isimplemented as:

[2243] (A>B? (A−B): A)

[2244] however this is only wrong when

[2245] A>(2B-1)

[2246] which will never occur.

[2247] B.4.6.4 Bmsnoop

[2248] The module, Bmsnoop, is composed of four eighteen bit supersnoopers that monitor the addresses supplied to the DRAM interface. Thesnooper must be “super” (i.e., can be accessed with the clocks running)to allow on chip testing of the external DRAM. These snoopers must workon a REQIACK system and are, therefore, different to any other on thedevice.

[2249] REQ/ACK is used on this interface, as opposed to a two-wireprotocol because it is essential to transmit information (i.e.,acknowledges) back to the sender which an accept will not do). Hence,this rigorously monitors the FIFO pointers.

[2250] B.4.7 Registers

[2251] To gain microprocessor write access to the initializationregisters, a one should be written to buf_access, and access will begiven when buf_access reads back one. Conversely, to give upmicroprocessor write access, zero should be written to buf_access.Access will be given when buf_access reads back zero. Note thatbuf_access is reset to one.

[2252] The dynamic and initialization registers of the present inventionmay be read at any time, however, to ensure that the dynamic registersare not changing the microprocessor, write access must be gained.

[2253] It is intended that the initialization registers be written toonly once. Re-writing them may cause the buffers to operate incorrectly.However, it is envisioned to increase the buffer length on-the-fly andto have the buffer manager use the new length when appropriate.

[2254] No check is ever made to see that the values in theinitialization registers are sensible, e.g., that the buffers do notoverlap. This is the user's responsibility. TABLE B.4.3 Buffer managernon-keyhole registers Register Name Usage Address CED_BUF_ACCESSxxxxxxxD 0x24 CED_BUF_KEYHOLE_ADDR xxDDDDDD 0x25 CED_BUF_KEYHOLEDDDDDDDD 0x26 CED_BUF_CB_WR_SNP_2 xxxxxxDD 0x54 CED_BUF_CB_WR_SNP_1DDDDDDDD 0x55 CED_BUF_CB_WR_SNP_0 DDDDDDDD 0x56 CED_BUF_CB_RD_SNP_2xxxxxxDD 0x57 CED_BUF_CB_RD_SNP_1 DDDDDDDD 0x58 CED_BUF_CB_RD_SNP_0DDDDDDDD 0x59 CED_BUF_TB_WR_SNP_2 xxxxxxDD 0x5a CED_BUF_TB_WR_SNP_1DDDDDDDD 0x5b CED_BUF_TB_WR_SNP_0 DDDDDDDD 0x5c CED_BUF_TB_RD_SNP_2xxxxxxDD 0x5d CED_BUF_TB_RD_SNP_1 DDDDDDDD 0x5e CED_BUF_TB_RD_SNP_0DDDDDDDD 0x5f

[2255] Where D indicates a register bit and x shows no register bit.TABLE B.4.4 Registers in buffer manager keyhole Keyhole Register NameUsage Keyhole Address CED_BUF_CB_BASE_3 xxxxxxxx 0x00 CED_BUF_CB_BASE_2xxxxxxDD 0x01 CED_BUF_CB_BASE_1 DDDDDDDD 0x02 CED_BUF_CB_BASE_0 DDDDDDDD0x03 CED_BUF_CB_LENGTH_3 xxxxxxxx 0x04 CED_BUF_CB_LENGTH_2 xxxxxxDD 0x05CED_BUF_CB_LENGTH_1 DDDDDDDD 0x06 CED_BUF_CB_LENGTH_0 DDDDDDDD 0x07CED_BUF_CB_READ_3 xxxxxxxx 0x08 CED_BUF_CB_READ_2 xxxxxxDD 0x09CED_BUF_CB_READ_1 DDDDDDDD 0x0a CED_BUF_CB_READ_0 DDDDDDDD 0x0bCED_BUF_CB_NUMBER_3 xxxxxxxx 0x0c CED_BUF_CB_NUMBER_2 xxxxxxDD 0x0dCED_BUF_CB_NUMBER_1 DDDDDDDD 0x0e CED_BUF_CB_NUMBER_0 DDDDDDDD 0x0fCED_BUF_TB_BASE_3 xxxxxxxx 0x10 CED_BUF_TB_BASE_2 xxxxxxDD 0x11CED_BUF_TB_BASE_1 DDDDDDDD 0x12 CED_BUF_TB_BASE_0 DDDDDDDD 0x13CED_BUF_TB_LENGTH_3 xxxxxxxx 0x14 CED_BUF_TB_LENGTH_2 xxxxxxDD 0x15CED_BUF_TB_LENGTH_1 DDDDDDDD 0x16 CED_BUF_TB_LENGTH_0 DDDDDDDD 0x17CED_BUF_TB_READ_3 xxxxxxxx 0x18 CED_BUF_TB_READ_2 xxxxxxDD 0x19CED_BUF_TB_READ_1 DDDDDDDD 0x1a CED_BUF_TB_READ_0 DDDDDDDD 0x1bCED_BUF_TB_NUMBER_3 xxxxxxxx 0x1c CED_BUF_TB_NUMBER_2 xxxxxxDD 0x1dCED_BUF_TB_NUMBER_1 DDDDDDDD 0x1e CED_BUF_TB_NUMBER_0 DDDDDDDD 0x1fCED_BUF_LIMIT_3 xxxxxxxx 0x20 CED_BUF_LIMIT_2 xxxxxxDD 0x21CED_BUF_LIMIT_1 DDDDDDDD 0x22 CED_BUF_LIMIT_0 DDDDDDDD 0x23 CED_BUF_CSRxxxxDDDD 0x24

[2256] B.4.8 Verification

[2257] Verification was conducted in Lsim with small FIFO's onto a dummyDRAM interface, and in C-code as part of the top level chip simulation.

[2258] B.4.9 Testing

[2259] Test coverage to the bman is through the snoopers in bmsnoop, thedynamic registers (shown in B.4.4) and using the scan chain which ispart of the DRAM interface scan chain.

[2260] SECTION B.5 Inverse Modeler

[2261] B.5.1 Introduction

[2262] This document describes the purpose, actions and implementationof the Inverse Modeller (imodel) and the Token Formatter (hsppk), inaccordance with the present invention.

[2263] Note: hsppk is a hierarchically part of the Huffman Decoder, butfunctionally part of the Inverse Modeller. It is, therefore, betterdiscussed in this section.

[2264] B.5.2 Overview

[2265] The Token buffer, which is between the imodel and hsppk, cancontain a great deal of data, all in off-chip DRAM. To ensure thatefficient use is made of this memory, the data must be in a 16 bitformat. The Formatter “packs” the data from the Huffman Decoder intothis format for the Token buffer. Subsequently, the Inverse Modeler“unpacks” data from the Token buffer format.

[2266] However, the Inverse Modeller's main function is the expandingout of “run/level” codes into a run of zero data followed by a level.Additionally, the Inverse Modeller ensures that DATA tokens have atleast 64 coefficients and it provides a “gate” for stopping streamswhich have not met their start-up criteria.

[2267] B.5.3 Interfaces

[2268] B.5.3.1 Hsppk

[2269] In the present invention, Hsppk has the Huffman Decoder as inputand the Token buffer as output. Both interfaces are of the two-wiretype, the input being a 17 bit token port, the output being 16 bit“packed data”, plus a FLUSH signal. In addition, Hsppk is clocked fromthe Huffman clock generator and, thus, connected to the Huffman scanchain.

[2270] B.5.3.2 Imodel

[2271] Imodel has the Token buffer start-up output gate logic (bsogl) asinputs and the Inverse Quantizer as output. Input from the Token bufferis 16 bit “packed data”, plus block_end signal, from the bsogl is onewirestream_enable. Output is an 11 bit token port. All interfaces arecontrolled by the two-wire interface protocol. Imodel has its own clockgenerator and scan chain.

[2272] Both blocks have microprocessor access only to the snoopers attheir outputs.

[2273] B.5.4 Block Description

[2274] B.b 5.4.1 Hsppk

[2275] Hsppk takes in the 17 bit data from the Huffman and outputs 16bit data to the Token buffer. This is achieved by first, eithertruncating or splitting the input data into 12 bit words, and second bypacking these words into a 16 bit format.

[2276] B.5.4.1.1 Splitting

[2277] Hsppk receives 17 bit data from the Inverse Huffman. This data isformatted into 12 bits using the following formats.

[2278] Where F=specifies format; E=extension bit; R=Run bit; L=lengthbit (in sign mag.) or non-DATA token bit; x=don't care.

[2279] FLLLLLLLLLLLFormat 0

[2280] ELLLLLLLLLLLFormat 0a

[2281] FRRRRRROO00000Format 1

[2282] Normal tokens only occupy the bottom 12 bits, having the form:

[2283] ExxxxxxLLLLLLLLLLL

[2284] This is truncated to format Oa However, DATA tokens have a runand a level in each word in the form:

[2285] ERRRRRRLLLLLLLLLLL.

[2286] This is broken in to the formats:

[2287] ERRRRRRLLLLLLLLLLL→FRRRRRR00000Format 1

[2288] ELLLLLLLLLLLFormat Oa

[2289] Or if the run is zero format 0 is used:

[2290] E000000LLLLLLLLLLL→FLLLLLLLLLLLFormat 0

[2291] It can be seen that in the format 0,the extension bit is lost andassumed to be one. Therefore, it cannot be used where the extension iszero. In this case, format 1 is unconditionally used.

[2292] B.5.4.1.2 Packing

[2293] After splitting, all data words are 12 bits wide. Every four 12bit words are “packed” into three 16 bit words: TABLE B.5.1 Packingmethod Input words Output words 000000000000 0000000000001111111111111111 1111111122222222 222222222222 2222333333333333 333333333333

[2294] B.5.4.1.3 Flushing of the Buffer

[2295] The DRAM interface of the present invention collects a block, 32sixteen bit “packed” words, before writing them to the buffer. Thisimplies that data can get stuck in the DRAM interface at the end of astream, if the block is only partially complete. Therefore a flushingmechanism is required. Accordingly, Hsppk signals the DRAM interface towrite it current partially complete block unconditionally.

[2296] B.5.4.2.1 Imup (UnPacker)

[2297] Imup performs three functions:

[2298] 4)Unpacking data from its sixteen bit format into 12 bit words.TABLE B.5.2 Unpacking method Input words Output words 0000000000001111000000000000 1111111122222222 111111111111 2222333333333333 222222222222333333333333

[2299] 5)Maintaining correct data during flushing of the Token buffer.

[2300] When the DRAM interface flushes, by unconditionally writing thecurrent partially complete block, rubbish data remains in the block. Theimup must delete rubbish data, i.e., delete all data from a FLUSH token,until the end of a block.

[2301] 6)Holding back data until Start-up Criteria are met.

[2302] Output of data from the block is conditional that a “valid”(stream_enable) is accepted from the Buffer Start-up for each differentstream. Consequently, twelve bit data is output to hsppk.

[2303] B.5.4.2.2 Imex (EXpander)

[2304] In the invention, Imex expands out all run length codes into runsof zeros followed by a level.

[2305] B.5.4.2.3 Impad (PADder)

[2306] Impad ensures that all DATA Token bodies contain 64 (or more)words. It does this by padding the last word of the Token with zeros.DATA Tokens are not checked for having over 64 words in the body.

[2307] B.5.5 Block Implementation

[2308] B.5.5.1 Hsppk

[2309] Typically, both the Splitting and packing is done in a singlecycle.

[2310] B.5.5.1.1 Splitting First, the format must be determined IF(datatoken) IF (lastformat = = 1) use format 0a; ELSE IF (run = = 0) useformat 0; ELSE use format 1; ELSE use format 0a; and format bitdetermined format 0 format bit = 0; format 0a format bit = extensionbit; format 1 format bit = 1;

[2311] If format 1 is used, no new data should be accepted in the nextcycle because the level of the code has yet to be output.

[2312] B.5.5.1.2 Packing

[2313] The packing procedure cycles every four valid data inputs. Thesixteen bit word output is formed from the last valid word, which isheld, and the succeeding word. If this is not valid, then the output isnot valid. The procedure is: TABLE B.5.3 Packing procedure Held WordSucceeding Word Packed Word valid cycle 0 xxxxxxxxxxxx 000000000000xxxxxxxxxxxxxxxx don't output valid cycle 1 000000000000 1111111111110000000000001111 output valid cycle 2 111111111111 2222222222221111111122222222 output valid cycle 3 222222222222 3333333333332222333333333333 output

[2314] Where x indicates undefined bits.

[2315] During valid cycle 0, no word is output because it is not valid.

[2316] The valid cycle number is maintained by a ring counter. It isincremented by valid data from the splitter and an accepted output.

[2317] When a FLUSH (or picture_end) token is received and the tokenitself is ready to output, a flush signal is also output to the DRAMinterface to reset the valid cycle to zero. If a FLUSH token arrives onanything but cycle 3, the flush signal must be delayed a valid cycle toensure the token itself it output.

[2318] B.5.5.2 Imodel

[2319] B.5.5.2.1 Imup (Unpacker)

[2320] As with the packer, the last valid input is stored, and combinedwith the next input, allows unpacking. TABLE B.5.4 Unpacking procedureSucceeding word Held Word Unpacked Word valid cycle 0 0000000000001111xxxxxxxxxxxxxxxx 000000000000 input valid cycle 1 11111111222222220000000000001111 111111111111 input valid cycle 2 22223333333333331111111122222222 222222222222 don't input valid cycle 3 22223333333333331111111122222222 333333333333 input

[2321] Where x indicates undefined bits

[2322] The valid cycle is maintained by a ring counter. The unpackeddata contains the token's data, flush and PICTURE_END decoded from it.Additionally, format and extension bit are decoded from the unpackeddata.

[2323] formatbit_is extn=(lastformat==1) 11 databody

[2324] format=databody && (formatbit && lastformatbit)

[2325] for token decoding and to be passed on to imex.

[2326] When a FLUSH (or picture end) token is unpacked and output toimex, all data is deleted (Valid forced low) until the block end signalis received from the DRAM interface.

[2327] B.5.5.2.2 Imex (EXpander)

[2328] In accordance with the present invention, imex is a four statemachine to expand run/level codes out. The state machine is:

[2329] state0: load run count from run code.

[2330] state 1: decrement run count, outputting zeros.

[2331] state 2: input data and output levels; default state.

[2332] state 3: illegal state.

[2333] B.5.5.2.3 Impad (PADder)

[2334] Impad is informed of DATA Token headers by imex. Next, it countsthe number of coefficients in the body of the token. If the token endsbefore there are 64 coefficients, zero coefficients are inserted at theend of the token to complete it to 64 coefficients. For example,unextended data headers have 64 zero coefficients inserted after them.DATA tokens with 64 or more coefficients are not affected by impad.

[2335] B.5.6 Registers

[2336] The imodel and hsppk of the present invention do not havemicroprocessor registers, with the exception of their snooper. TABLEB.5.5 Imodel & hsppk registers Register Name Usage Address CED_H_SNP_2VAxxxxxx 0x49 CED_H_SNP_1 DDDDDDDD 0x4a CED_H_SNP_0 DDDDDDDD 0x4bCED_IM_SNP_1 VAExxDDD 0x4a CED_IM_SNP_0 DDDDDDDD 0x4d

[2337] Where V=valid bit; A=accept bit; E=extension bit; D=data bit.

[2338] B.5.7 Verification

[2339] Selected streams run through Lsim simulations.

[2340] B.b 5.8 Testing

[2341] Test coverage to the imodel at the input is through the Tokenbuffer output snooper, and at the output through the imodel's ownsnooper. Logic is covered the imodel's own scan chain.

[2342] The output of the hsppk is accessible through the huffman outputsnooper. The logic is visible through the huffman scan chain.

[2343] SECTION B.6 Buffer Start-up

[2344] B.6.1 Introduction

[2345] This section describes the method and implementation of thebuffer start-up in accordance with the present invention.

[2346] B.6.2 Overview

[2347] To ensure that a stream of pictures can be displayed smoothly andcontinuously a certain amount of data must be gathered before decodingcan start. This is called the start-up condition. The coding standardspecifies a VBV delay which can be translated, approximately, into theamount of data needed to be gathered. It is the purpose of the “BufferStart-up” to ensure that every stream fulfills its start-up conditionbefore its data progresses from the token buffer, allowing decoding. Itis held in the buffers by a notional gate (the output gate) at theoutput of the token buffer (i.e., in the Inverse Modeler). This gatewill only be open for the stream once its start-up condition has beenmet.

[2348] B.6.3 Interfaces

[2349] Bscntbit (Buffer Start-up bit counter) is in the datapath, andcommunicates by two-wire interfaces, and is connected to themicroprocessor. It also branches with a two-wire interface to bsogl(Buffer Start-up Output Gate Logic). Bsogl via a two-wire interfacecontrols imup (Inverse Modeler UnPacker), which implements the outputgate.

[2350] B.6.4 Block Structure

[2351] As shown in FIG. 130, Bscntbit lies in the datapath between theStart Code Detector and the coded data buffer. This single cycle blockcounts the valid words of data leaving the block and compares thisnumber with the start-up condition (or target) which will be loaded fromthe microprocessor. When the target is met, bsogl is informed. Data isunaffected by bscntbit.

[2352] Bsogl lies between bscntbit and imup (in the inverse modeler). Ineffect, it is a queue of indicators that streams have met their targets.The queue is moved along by streams leaving the buffers (i.e., FLUSHtokens received in the data stream at imup), when another “indicator” isaccepted by imup. If the queue is empty (i.e., there are no streams inthe buffers which have yet met their start-up target) the stream in imupis stalled.

[2353] The queue only has a finite depth, however, this may beindefinitely expanded by breaking the queue in bsogl and allowing themicroprocessor to monitor the queue. These queue mechanisms are referredto as internal and external queues respectively.

[2354] B.6.5 Block Implementation

[2355] B.6.5.1 Bsbitcnt (Buffer Start-up bit counter)

[2356] Bscntbit counts all the valid words that are input into thebuffer start-up. The counter (bsctr) is a programmable counter of 16-24bits width. Moreover, bsctr has carry look ahead circuitry to give itsufficient speed. Bsctr's width is programmed by ced_bs_prescale. Itdoes this by forcing bits 8-16 high, which makes them always pass acarry. They are, therefore, effectively not used. only the top eightbits of bsctr are used for comparisons with the target (ced_bs_target).

[2357] The comparison (ced_bs_count>=ced_bs_target) is done by bscmp.

[2358] The target is derived from the stream when the stream is in theHuffman Decoder and calculated by the microprocessor. It will,therefore, only be set sometime after the start of the stream. Beforestart-up, the target_valid is set low. writing to ced_bs_target setstarget_valid high and allows comparisons in bscmp to take place. Whenthe comparison shows ced_bs_count>=ced_(—bs)_target, target_valid is setlow. The target has been met.

[2359] When the target is met the count is reset. Note, it is not resetat the end of a stream. In addition, counting is disabled after thetarget is met if it is before the end of the stream. The count saturatesto 255.

[2360] When a stream ends (i.e., a flush) is detected in bsbitcnt, anabs_flush_event is generated. If the stream ends before the target ismet, an additional event is also generated(bs_flush_before_target_met_event). When any of these events occur, theblock is stalled. This allows the user to recommence the search for thenext stream's target or in the case of abs_flush_before_target_met_event event either:

[2361] 1)write a target of zero which will force a target_met or

[2362] 2)note that target was not met and allow the next stream toproceed until this combined with the last stream reaches the target. Thetarget for this next stream can should adjusted accordingly.

[2363] B.6.5.2 BSOGL (Buffer Start-up Output Gate Logic)

[2364] As previously described, Bsogl is a queue of indicators that astream has met its target. The queue type is set by ced_bs_queue(internal(0) or external(1)). This is a reset to select an internalqueue. The depth of the queue determines the maximum number of satisfiedstreams that can be in the coded data buffer, Huffman, and token buffer.When this number is reached (i.e. the queue is full) bsogl will forcethe datapath to stall at bsbitcnt.

[2365] Using an internal queue requires no action from themicroprocessor. However, if it is necessary to increase the depth of thequeue, an external queue can be set (by setting ced_bs_access to gainaccess to ced_bs_queue which should be set, target_met_event andstream_end_event enabled and access relinquished).

[2366] The external queue (a count maintained by the microprocessor) isinserted into the internal queue. The external queue is maintained bytwo events. target_met_event and stream_end_event. These can simply bereferred to as service_queue_input and service_queue_outputrespectively] and a register ced_bs_enable_nxt_stream. In effect,target_met_event is the up stream end of the internal queue supplyingthe queue. Similarly, ced_bs_enable_nxt_stream is the down stream end ofthe internal queue consuming the queue. Similarly, stream_end_event is arequest to supply the down stream queue; stream_end_event resetsced_bs_enable_nxt_stream. The two events should be serviced as follows:/* TARGET_MET_EVENT */ j = micro_read(CED_BS_ENABLE_NXT_STM); if (j ==0) /* Is next stream enabled \*/ {/*no, enable it*/micro_write(CED_BS_ENABLE_NXT_STM, 1); printf(“ enable next stream(queue = 0x%x)\n”, (context→queue; } else /“yes, increment the queue of“target_met” streams”/ { queue++; printf(“ stream already enabled (queue= 0x%x)\n”, (context- >queue)); } /* STREAM_EVENT */ if (queue > 0)/*are there any “target_mets ” left\ */ {/*yes, decrement the queue andenable another stream */ queue−−; micro_write (CED_BS_ENABLE_NXT_STM,1); printf(“ enable next stream (queue = 0x%x)\n”, (context→queue } elseprintf(“ queue empty cannot enable next stream (queue = 0x%x)\n”,queue); micro_write(CED_EVENT_1, 1 << BS_STREAM_END_EVENT); /* clearevent */

[2367] The queue type can be changed from internal to external at anytime (by the means described above), but they can only be changedexternal to internal when the external queue is empty (from above“queue==0”), by setting ced_bs_access to gain access to ced_bs_queuewhich should be reset, target_met_event and stream_end_event masked, andaccess relinquished.

[2368] On the other hand, disable checking of stream start-upconditions, set ced_bs_queue (external), mask target_met_event andstream_end_event and set ced_bs_enable_nxt_stream. In this way, allstreams will always be enabled.

[2369] B.6.6 Microprocessor Registers TABLE B.6.1 Bscntbit registersRegister name Usage Address CED_BS_ACCESS xxxxxxxD 0x10 CED_BS_PRESCALE*xxxxxDDD 0x11 CED_BS_TARGET* DDDDDDDD 0x12 CED_BS_COUNT* DDDDDDDD 0x13BS_FLUSH_EVENT rrrrrDrr 0x02 BS_FLUSH_MASK rrrrrDrr 0x03BS_FLUSH_BEFORE_TARGET_(—) rrrrDrrr 0x02 MET_EVENTBS_FLUSH_BEFORE_TARGET_(—) rrrrDrrr 0x03 MET_MASK

[2370] TABLE B.6.2 Bsogl registers Register name Usage AddressTARGET_MET_EVENT rrrDrrrr 0x02 TARGET_MET_MASK rrrDrrrr 0x03STREAM_END_EVENT rrDrrrrr 0x02 STREAM_END_MASK rrDrrrrr 0x03CED_BS_QUEUE* xxxxxxxD 0x14 CED_BS_ENABLE_NXT_STM* xxxxxxxD 0x15

[2371] SECTION B7 The DRAM Interface

[2372] B.7.1 Overview

[2373] In the present invention, the Spatial Decoder, Temporal Decoderand Video Formatter each contain a DRAM interface block for thatparticular chip. In all three devices, the function of the DRAMinterface is to transfer data from the chip to the external DRAM andfrom the external DRAM into the chip via block addresses supplied by anaddress generator.

[2374] The DRAM interface typically operates from a clock which isasynchronous to both the address generator and to the clocks of thevarious blocks through which data is passed. This asynchronism isreadily managed, however, because the clocks are operating atapproximately the same frequency.

[2375] Data is usually transferred between the DRAM Interface and therest of the chip in blocks of 64 bytes (the only exception beingprediction data in the Temporal Decoder). Transfers take place by meansof a device known as a “swing buffer”. This is essentially a pair ofRAMs operated in a double-buffered configuration, with the DRAMinterface filling or emptying one RAM while another part of the chipempties or fills the other RAM. A separate bus which carries an addressfrom an address generator is associated with each swing buffer.

[2376] Each of the chips has four swing buffers, but the function ofthese swing buffers is different in each case. In the Spatial Decoder,one swing buffer is used to transfer coded data to the DRAM, another toread coded data from the DRAM, the third to transfer tokenized data tothe DRAM and the fourth to read tokenized data from the DRAM. In theTemporal Decoder, one swing buffer is used to write Intra or Predictedpicture data to the DRAM, the second to read Intra or Predicted datafrom the DRAM and the other two to read forward and backward predictiondata. In the Video Formatter, one swing buffer is used to transfer datato the DRAM and the other three are used to read data from the DRAM, onefor each of Luminance (Y) and the Red and Blue color difference data (Crand Cb, respectively).

[2377] The following section describes the operation of a DRAM interfacein accordance with the present invention, which has one write swingbuffer and one read swing buffer, which is essentially the same as theoperation of the Spatial Decoder DRAM Interface. This is illustrated inFIG. 131, “DRAM Interface,”.

[2378] B.7.2 A Generic DRAK Interface

[2379] Referring to FIG. 131, the interfaces to the address generator420 and to the blocks which supply and take the data are all two wireinterfaces. The address generator 420 may either generate addresses asthe result of receiving control tokens, or it may merely generate afixed sequence of addresses. The DRAM interface 421 treats the two wireinterfaces associated with the address generator in a special way.Instead of keeping the accept line high when it is ready to receive anaddress, it waits for the address generator to supply a valid address,processes that address and then sets the accept line high for one clockperiod. Thus, it implements a request/acknowledge (REQ/ACK) protocol.

[2380] A unique feature of the DRAM Interface is its ability tocommunicate with the address generator and the blocks which provide oraccept the data completely independent of the other. For example, theaddress generator may generate an address associated with the data inthe write swing buffer, but no action will be taken until the writeswing buffer signals that there is a block of data which is ready to bewritten to the external DRAM 422. However, no action is taken until anaddress is supplied on the appropriate bus from the address generator.Further, once one of the RAMs in the write swing buffer has been filledwith data, the other may be completely filled and “swung” to the DRAMInterface side before the data input is stalled (the two-wire interfaceaccept signal set low).

[2381] In understanding the operation of the DRAM Interface of thepresent invention, it is important to note that in a properly configuredsystem the DRAM Interface will be able to transfer data between theswing buffers and the external DRAM at least as fast as the sum of allthe average data rates between the swing buffers and the rest of thechip.

[2382] Each DRAM Interface contains a method of determining which swingbuffer it will service next. In general, this will be either a “roundrobin”, in which the swing buffer which is serviced is the nextavailable swing buffer which has less recently had a turn, or a priorityencoder in which some swing buffers have a higher priority than others.In both cases, an additional request will come from a refresh requestgenerator which has a higher priority than all the other requests. Therefresh request is generated from a refresh counter which can beprogrammed via the microprocessor interface.

[2383] B.7.2.1 The Swing Buffers

[2384]FIG. 132 illustrates a write swing buffer. The operation is asfollows:

[2385] 1)Valid data is presented at the input 430 (data in). As eachpiece of data is accepted it is written into RAM1 and the address isincremented.

[2386] 2)When RAM1 is full, the input side gives up control and sends asignal to the read side to indicate that RAM1 is now ready to be read.This signal passes between two asynchronous clock regimes, and so passesthrough three synchronizing flip-flops.

[2387] 3)The next item of data to arrive on the input side is writteninto RAM2, which is still empty.

[2388] 4)When the round robin or priority encoder indicates that it isthe turn of this swing buffer to be read, the DRAM Interface reads thecontents of RAM1 and writes them to the external DRAM. A signal is thensent back across the asynchronous interface, as in (2), to indicate thatRAM1 is now ready to be filled again.

[2389] 5)If the DRAM Interface empties RAMI and “swings” it before theinput side has filled RAM2, then data can be accepted by the swingbuffer continually, otherwise when RAM2 is filled the swing buffer willset its accept signal low until RAMi has been “swung” back for use bythe input side.

[2390] 6)This process is repeated ad infinitum.

[2391] The operation of a read swing buffer is similar, but with inputand output data busses reversed.

[2392] B.7.2.2 Addressing of External DRAM and Swing Buffers

[2393] The DRAM Interface is designed to maximize the available memorybandwidth. Consequently, it is arranged so that each 8×3 block of datais stored in the same DRAM page. In this way full use can be made ofDRAM fast page access modes, where one row address is supplied followedby many column addresses. In addition, a facility is provided to allowthe data bus to the external DRAM to be 8, 16 or 32 bits wide, so thatthe amount of DRAM used can be matched to the size and bandwidthrequirements of the particular application.

[2394] In this example (which is exactly how the DRAM Interface on theSpatial Decoder works), the address generator provides the DRAMInterface with block addresses for each of the read and write swingbuffers. This address is used as the row address for the DRAM. The sixbits of column address are supplied by the DRAM Interface itself, andthese bits are also used as the address for the swing buffer RAM. Thedata bus to the swing buffers is 32 bits wide, so if the bus width tothe external DRAM is less than 32 bits, two or four external DRAMaccesses must be made before the next word is read from a write swingbuffer or the next word is written to a read swing buffer (read andwrite refer to the direction of transfer relative to the external DRAM).

[2395] The situation is more complex in the cases of the TemporalDecoder and the Video Formatter. These are covered separately below.

[2396] B.7.3 DRAM Interface Timing

[2397] In the present invention, the DRAM Interface Timing block usestiming chains to place the edges of the DRAM signals to a precision of aquarter of the system clock period. Two quadrature clocks from the phaselocked loop are used. These are combined to form a notional 2× clock.Any one chain is then made from two shift registers in parallel, onopposite phases of the “2× clock”.

[2398] First of all, there is one chain for the page start cycle andanother for the read/write/refresh cycles. The length of each cycle isprogrammable via the microprocessor interface, after which the pagestart chain has a fixed length, and the cycle chain's length changes asappropriate during a page start.

[2399] On reset, the chains are cleared and a pulse is created. Thispulse travels along the chains, being directed by the state informationfrom the DRAM Interface. The DRAM Interface clock is generated by thispulse. Each DRAM Interface clock period corresponds to one cycle of theDRAM. Thus, as the DRAM cycles have different lengths, the DRAMInterface clock is not at a constant rate.

[2400] Further, timing chains combine the pulse from the above chainswith the information from DRAM Interface to generate the output strobesand enables (notcas, notras, notwe, notoe).

[2401] SECTION B.8 Inverse Quantizer

[2402] B.8.1 Introduction

[2403] This document describes the purpose, actions and implementationof the inverse quantizer, (iq) in accordance with the present invention.

[2404] B.8.2 Overview

[2405] The inverse quantizer reconstructs coefficients from quantizedcoefficients, quantization weights and step sizes, all of which aretransmitted within the datastream.

[2406] B.8.3 Interfaces

[2407] The iq lies between the inverse modeler and the inverse DCT inthe datapath and is connected to a microprocessor. Datapath connectionsare via two-wire interfaces. Input data is 10 bits wide, output is 11bits wide.

[2408] B.8.4 Mathematics of Inverse Quantization

[2409] B.8.4.1 H261 Equations

[2410] For blocks coded in intra mode: $\begin{matrix}\begin{matrix}{C_{i}^{*} = {8Q_{i}}} & {i = 0}\end{matrix} \\\begin{matrix}{{ \begin{matrix}{C_{i}^{*} = {{iq\_ quant}{{\_ scale}\lbrack {{2Q_{i}} + {{sign}( Q_{i} )}} \rbrack}}} \\\begin{matrix}{C_{i}^{*} = {C_{i}^{*} - {{sign}( C_{i}^{*} )}}} & {C_{i}^{*} = {even}}\end{matrix} \\\begin{matrix}{C_{i}^{*} = C_{i}^{*}} & {C_{i}^{*} = {odd}}\end{matrix}\end{matrix} \} 0} < i < 64} \\{C_{i} = {\min ( {{\max ( {C_{i^{*}}^{*} - 2048} )}{.2047}} )}}\end{matrix}\end{matrix}$

[2411] For all other coded blocks: $\begin{matrix}{{ \begin{matrix}{C_{i}^{*} = {{iq\_ quant}{{\_ scale}\lbrack {{2Q_{i}} + {{sign}( Q_{i} )}} \rbrack}}} \\\begin{matrix}{C_{i}^{*} = {C_{i}^{*} - {{sign}( C_{i}^{*} )}}} & {C_{i}^{*} = {even}}\end{matrix} \\\begin{matrix}{C_{i}^{*} = C_{i}^{*}} & {C_{i}^{*} = {odd}}\end{matrix}\end{matrix} \} 0} \leq i < 64} \\{C_{i} = {\min ( {{\max ( {C_{i^{*}}^{*} - 2048} )}{.2047}} )}}\end{matrix}$

[2412] B.8.4.2 JPEG Equations

C′ _(i) =W _(i,j) Q _(i)+1024i=0

C′ _(i) =W _(i,j) Q _(i)0<i<64

C _(i)=min(max(C′ _(i′)-2048).2047)

j=jpeg_table_indirection(c)

[2413] B.8.4.3 MPEG Equations

[2414] For blocks coded in intra mode: $\begin{matrix}\begin{matrix}{C_{i}^{*} = {{W_{i,j}Q_{i}} + 1024}} & {i = 0}\end{matrix} \\\begin{matrix}{ \begin{matrix}{C_{i}^{*} = {{floor}( \frac{2{iq\_ quant}{\_ scale}\quad W_{i,j}Q_{i}}{16} )}} \\\begin{matrix}{C_{i}^{*} = {C_{i}^{*} - {{sign}( C_{i}^{*} )}}} & {C_{i}^{*} = {even}}\end{matrix} \\\begin{matrix}{C_{i}^{*} = C_{i}^{*}} & {C_{i}^{*} = {odd}}\end{matrix}\end{matrix} \} \begin{matrix}{0 < i < 64} \\{j = 0.2}\end{matrix}} \\{C_{i} = {\min ( {{\max ( {C_{i^{*}}^{*} - 2048} )}{.2047}} )}}\end{matrix}\end{matrix}$

[2415] 1024 is added in intra DC case to account for predictors inhuffrnan being reset to zero. For all other coded blocks:$\begin{matrix}{ \begin{matrix}{C_{i}^{*} = {{floor}( \frac{{iq\_ quant}{\_ scale}\quad {W_{i,j}( {{2Q_{i}} + {{sign}( Q_{i} )}} )}}{16} )}} \\\begin{matrix}{C_{i}^{*} = {C_{i}^{*} - {{sign}( C_{i}^{*} )}}} & {C_{i}^{*} = {even}}\end{matrix} \\\begin{matrix}{C_{i}^{*} = C_{i}^{*}} & {C_{i}^{*} = {odd}}\end{matrix}\end{matrix} \} \begin{matrix}{0 < i < 64} \\{j = 1.3}\end{matrix}} \\{C_{i} = {\min ( {{\max ( {C_{i^{*}}^{*} - 2048} )}{.2047}} )}}\end{matrix}$

[2416] B.8.4.4 JPEG Variation Equations $\begin{matrix}\begin{matrix}{C_{i}^{*} = {{{floor}( \frac{2{iq\_ quant}{\_ scale}\quad W_{i,j}Q_{i}}{16} )} + 1024}} & {i = 0} \\{C_{i}^{*} = {{floor}( \frac{2{iq\_ quant}{\_ scale}\quad W_{i,j}Q_{i}}{16} )}} & {0 < i < 64}\end{matrix} \\{C_{i} = {\min ( {{\max ( {C_{i^{*}}^{*} - 2048} )}{.2047}} )}} \\{j = {{jpeg\_ table}{\_ indirection}(c)}}\end{matrix}$

[2417] B.8.4.5 All Other Tokens

[2418] All tokens except DATA Tokens must pass through the iqunquantized

[2419] Where: $\begin{matrix}{{{sign}(a)} = \{ \begin{matrix}{- 1} & {a < 0} \\0 & {a = 0} \\1 & {a > 0}\end{matrix} } \\{{\max ( {a,b} )} = \{ \begin{matrix}a & {a > b} \\b & {a \leq b}\end{matrix} } \\{{\min ( {a,b} )} = \{ \begin{matrix}a & {a \leq b} \\b & {a > b}\end{matrix} }\end{matrix}$

[2420] Floor(a) returns an integer such that:

[2421] (a−1)<floor (a)≦a> a≧0

[2422] a≦floor(a)<(a+1) a≧0

[2423] O_(i) are the quantized coefficients.

[2424] C_(i) are the reconstructed coefficients

[2425] W_(i,j) are the values in the quantisation table matrices

[2426] i is the coefficient index along the zig-zag

[2427] j is the quantisation table matrix number (0<=j<=3)

[2428] B.8.4.6 Multiple Standards Combined

[2429] It can be shown that all the above standards and their variations(also control data which must be unchanged by the iq) can be mapped onto single equation:${OUTPUT} = \frac{( {{2{INPUT}} + k} )({xy})}{16}$

[2430] With the additional post inverse quantisation functions of:

[2431] Add 1024

[2432] Convert from sign magnitude to 2's complement representation,

[2433] Round all even numbers to the nearest odd number towards zero.

[2434] Saturate result to +2047 or −2048.

[2435] The variables k, x and y for each variation of the standards andwhich functions they use is shown in Table 3.8.1.

[2436] B.8.4.6 Multiple Standards Combined TABLE B8.1 Control decoding zy Add Round Sat. Convert Standard Weight Scale k 1024 Even Res't 2'scomp H261 intra DC  8 8 0 No No Yes Yes intra 16 iq_quant_scale 1 No YesYes Yes other 16 iq_quant_scale 1 No Yes Yes Yes JPEG DC W_(i)  8 0 YesNo Yes Yes other W_(i)  8 0 No No Yes Yes MPEG intraDC 8 8 0 Yes No YesYes intra W_(i) iq_quant_scale 0 No No Yes Yes other W_(i)iq_quant_scale 1 No Yes Yes Yes XXX DC W_(i) iq_quant_scale 0 Yes No YesYes other W_(i) iq_quant_scale 0 No No Yes Yes Other Tokens  1 8 0 No NoNo No

[2437] B.8.5 Block Structure

[2438] From B.8.4.6 and Table B.8.1, it can be seen that a singlearchitecture can be used for a multi-standard inverse quantizer. Itsarithmetic block diagram is shown in FIG. 133 “Arithmetic Block”:

[2439] Control for the arithmetic block can be functionally broken intotwo sections:

[2440] Decoding of tokens to load status registers or quantizationtables.

[2441] Decoding of the status registers into control signals.

[2442] Tokens are decoded in iqca which controls the next cycle, i.e.,iqcb's bank of registers. It also controls the access to the fourquantization tables in igram. The arithmetic, that is, two multipliersand the post functions, are in iqarith. The complete block diagram forthe iq is shown in FIG. 134.

[2443] B.8.6 Block Implementation

[2444] B.8.6.1 Iqca

[2445] In the invention, iqca is a state machine used to decode tokensinto control signals for igram and the register in iqcb. The statemachine is better described as a state machine for each token since itis reset by each new token. For example:

[2446] The code for the QUANT_SCALE (see B.8.7.4, “QUANT_SCALE”) andQUANT_TABLE (see B.8.7.6, “QUANT_TABLE”) are as follows: if (tokenheader= = QUANT_SCALE) { sprintf(preport, “QUANT_SCALE”); reg_addr =ADDR_IQ_QUANT_SCALE; rnotw = WRITE; enable = 1; } if (tokenheader = =QUANT_TABLE) /*QUANT_TABLE token */ switch (substate) { case 0: /*quantisation table header */ sprintf(preport, “QUANT_TABLE_%s_s0”,(headerextn ? “(full)” : “(empty)”)); nextsubstate = 1; insertnext =(headerextn ? 0 : 1); reg_addr = ADDR_IQ_COMPONENT; rnotw = WRITE;enable = 1; break; case 1: /* quantisation table body */sprintf(preport, “QUANT_TABLE_%s_s1”, (headerextn ? “(full)” :“(empty)”)); nextsubstate = 1; insertnext = (headerextn ? 0 :(qtm_addr_63 = = 0)); reg_addr = USE_QTM; rnotw = (headerextn ? WRITE :READ); enable = 1; break; default; sprintf(preport, “ERROR in iqquantisation table tokendecoder (substate %x)\n*, substate); break; } }

[2447] Where a substate is a state within a token, QUANT_SCALE has, forexample, only one substate. However, the QUANT_TABLE has two, one beingthe header, the second the token body.

[2448] The state machine is implemented as a PLA. Unrecognized tokenscause no wordline to rise and the PLA to output default (harmless)controls.

[2449] Additionally, iqca supplies addresses to igram from BodyWordcounter and inserts words into the stream, for example in an unextendedQUANT_TABLE (see B.8.7.4). This is achieved by stalling the input whilemaintaining the output valid. The words can be filled with the correctdata in succeeding blocks (iqcb or iqarith).

[2450] iqca is a single cycle in the datapath controlled by two-wireinterfaces.

[2451] B.8.6.2 iqcb

[2452] In the invention, iqcb holds the iq status registers. Under thecontrol of iqca it loads or unloads these from/to the datapath.

[2453] The status registers are decoded (see Table B.8.1) into controlwires for iqarith; to control the XY multiplier terms and the postquantization functions.

[2454] The sign bit of the datapath is separated here and sent to thepost quantization functions. Also, zero valued words on the datapath aredetected here. The arithmetic is then ignored and zero muxed onto thedatapath. This is the easiest way to comply with the “zero in; zero out”spec of the iq.

[2455] The status registers are accessible from the microprocessor onlywhen the register iq_access has been set to one and reads back one. Inthis situation, iqcb has halted the datapath, thus ensuring theregisters have a stable value and no data is corrupted in the datapath.

[2456] Iqcb is a single cycle in the datapath controlled by two wireinterfaces.

[2457] B.8.6.3 Iqram

[2458] Iqram must hold up to four quantization table matrices (QTM),each 64*8 bits. It is, therefore, a 256*8 bits six transistor RAM,capable of one read or one write per cycle.

[2459] The RAM is enclosed by two-wire interface logic receiving itscontrol and write data from iqca. It reads out data to iqarith.Similarly, igran occupies the same cycle in the datapath as iqcb.

[2460] The RAM may be read and written from the microprocessor wheniq_access reads back one. The RAM is placed behind a keyhole register,iq_qtm_keyhole and addressed by iq_qtm_keyhole_addr. Accessingiq_qtm_keyhole will cause the address to which it points, held iniq_qtm_keyhole_addr to be incremented. Likewise, iq_qtm_keyhole_addr canbe written to directly.

[2461] B.8.6.4 iqarith

[2462] Note, iqarith is three functions pipelined and split over threecycles. The functions are discussed below (see FIG. 133).

[2463] B.8.6.4.1 XY Multiplier

[2464] This is a 5(X) by 8(Y) bit carry save unsigned multiplier feedingon to the datapath multiplier. The multiplier and multiplicand areselected with control wires from iqcb. The multiplication is in thefirst cycle, the resolving adder in the second.

[2465] At the input to the multiplier, data from iqram can be muxed ontothe datapath to read a QUANT_TABLE out onto the datapath.

[2466] B.8.6.4.2 (XY)* Datapath Multiplier

[2467] This 13 (XY) by 12 (datapath) bit carry save unsigned multiplieris split over the three cycles of the block. Three partial products inthe first cycle, seven in the second and the remaining two in the third.

[2468] Since all output from the multiplier is less than 2047(non_coefficient) or saturated to +2047/−2048, the top twelve bits don'tever need to be resolved. Accordingly, the resolving adder is just twobits wide. On the remainder of the high order bits, a zero detectsuffices as a saturate signal.

[2469] B.8.6.4.3 Post Quantization Functions

[2470] The post quantization functions are

[2471] Add 1024

[2472] Convert from sign magnitude to 2's complement representation.

[2473] Round all even numbers to the nearest odd number towards zero.

[2474] Saturate result to +2047 or −2048.

[2475] Set output to zero (see B.8.6.2)

[2476] The first three functions are implemented on a 12 bit adder(pipelined over the second and third cycles). From this, it can be seenwhat each function requires and these are then combined onto the singleadder. TABLE B.8.2 Post quantization adder functions Function ifdatapath > 0 if datapath > 0 Convert to 2's complement nothing invertadd one Round all even numbers subtract one add one Add 1024 add 1024add 1024

[2477] As will be appreciated by one of ordinary skill in the art, careshould be taken when reprogramming these functions as they are veryinterdependent when comnbined.

[2478] The saturate values, zero and zero+1024 are muxed onto thedatapath at the end of the third cycle.

[2479] B.8.7 Inverse Quantizer Tokens

[2480] The following notes define the behavior of the Inverse Quantizerfor each Token tp which it responds. In all cases, the Tokens are alsotransported to the output of the Inverse Quantizer. In most cases, theToken is unmodified by the Inverse Quantizer with the exceptions asnoted below. All unrecognized Tokens are passed unmodified to the outputof the Inverse Quantizer.

[2481] B.8.7.1 SEQUENCE START

[2482] This Token causes the registers iq_prediction mode[1:0] andiq_mpeg_indirection[1:0] to be reset to zero.

[2483] B.8.7.2 CODING_STANDARD

[2484] This Token causes iqstandard[1:0] to be loaded with theappropriate value based upon the current standard (MPEG, JPEG or H.261)being decoded.

[2485] B.8.7.3 PREDICTION_MODE

[2486] This Token loads iq-prediction_mode[1:0]. Although thePREDICTION_MODE Token carries more than two bits, the Inverse Quantizeronly needs access to the two lowest order bits. These determine whetheror not the block is intra coded.

[2487] B.8.7.4 QUANT_SCALE

[2488] This Token loads iq_quant_scale[4:0].

[2489] B.8.7.5 DATA

[2490] In the present invention, this Token carries the actual quantizedcoefficients. The head of the token contains two bits identifying thecolor component and these are loaded into iq_component[1:0]. The nextsixty four Token words contain the quantized coefficients. These aremodified as a result of the inverse quantization process and arereplaced by the reconstructed coefficients.

[2491] If exactly sixty four extension words are not present in theToken, the behavior of the Inverse Quantizer is undefined.

[2492] The DATA Token at the input of the Inverse Quantizer carriesquantized coefficients. These are represented in eleven bits in asign-magnitude format (ten bits plus a sign bit). The value “minus zero”should not be used but is correctly interpreted as zero.

[2493] The DATA Token at the output of the Inverse Quantizer carriesreconstructed coefficients. These are represented in twelve bits in atwos complement format (eleven bits plus a sign bit). The DATA Token atthe output will have the same number of Token Extension words as it hadat the input of the Inverse Quantizer.

[2494] B.8.7.6 QUANT_TABLE

[2495] This Token may be used to load a new quantization table or toread out an existing table. Typically, in the Inverse Quantizer, theToken will be used to load a new table which has been decoded from thebit stream. The action of reading out an existing table is useful in theforward quantizer of an encoder if that table is to be encoded into thebit stream.

[2496] The Token Head contains two bits identifying the table numberthat is to be used. These are placed in iq_component[1:0]. Note thatthis register now contains a “table number” not a color component.

[2497] If the extension bit of the Token Head is one, the InverseQuantizer expects there to be exactly sixty four extension Token Words.Each one is interpreted as a quantization table value and placed in asuccessive location of the appropriate table, starting at location zero.The ninth bit of each extension Token word is ignored. The Token is alsopassed to the output of the Inverse Quantizer, unmodified, in the normalway.

[2498] If the extension bit of the Token Head is zero, then the InverseQuantizer will read out successive locations of the appropriate tablestarting at location zero. Each location becomes an extension Token word(the ninth bit will be zero). At the end of this operation, the Tokenwill contain exactly sixty four extension Token words.

[2499] The operation of the Inverse Quantizer in response to this tokenis undefined for all numbers of extension words except zero and sixtyfour.

[2500] B.8.7.7 JPEG_TABLE_SELECT

[2501] This token is used to load or unload translations of colorcomponents to table numbers to/from iq_ipeg_indirection. Thesetranslations are used in JPEG and other standards.

[2502] The Token Head contains two bits identifying the color componentthat is currently of interest. These are placed in iq component[1:0].

[2503] If the extension bit of the Token Head is one, the Token shouldcontain one extension word, the lowest two bits of which are writteninto the iq_ipeg_indirection[2*iq_component[1:0]+1:2*iq_component[1:0]]location. The value just read becomes a Token extension word (theupper seven bits will be zero). At the end of this operation, the Tokenwill contain exactly one Token extension word. TABLE B.8.3JPEG_TABLE_SELECT action Colour component in reader bits ofiq_ipeg_indirection accessed 0 [1:0] 1 [3:2] 2 [5:4] 3 [7:6]

[2504] B.8.7.8 MPEG_TABLE_SELECT

[2505] This Token is used to define whether to use the default or userdef ined quantization tables while processing via the MPEG standard. TheToken Head contains two bits. Bit zero of the header determines whichbit if iq_mpeg_indirection is written into. Bit one is written into thatlocation.

[2506] Since the iq_mpeg_indirection[1:0] register is cleared by theSEQUENCE_START Token, it will only be necessary to use this Token if auser defined quantization table has been transmitted in the bit stream.

[2507] B.8.8 Microprocessor Registers

[2508] B.8.s.1 iq_access

[2509] To gain microprocessor access to any of the iq registers,iq_access must be set to one and polled until it reads back one (seeB.8.6.2). Failure to do this will result in the registers being readstill being controlled by the datapath and, therefore, not being stable.In the case of the igram, the accesses are locked out, reading backzeros.

[2510] Writing zero to iq_access relinquishes control back to thedatapath.

[2511] B.8.8.2 Iq_coding_standard[1:0]

[2512] This register holds the coding standard that is being implementedby the Inverse Quantizer. TABLE B.8.4 Coding standard valuesiq_coding_standard Coding Standard 0 H.261 1 JPEG 2 MPEG 3 XXX

[2513] This register is loaded by the CODING_STANDARD Token.

[2514] Although this is a two bit register, at present eight bits areallocated in the memory map and future implementations can deal withmore than the above standards.

[2515] B.8.8.3 Iq_mpeg_indirection[1:0]

[2516] This two bit register is used during MPEG decoding operations tomaintain a record of which quantization tables are to be used.

[2517] Iq_mpeg_indirection[0] controls the table that is used for intracoded blocks. If it is zero then quantization table 0 is used and isexpected to contain the default quantization table. If it is one, thenquantization table 2 is used and is expected to contain the user definedquantization table for intra coded blocks.

[2518] This register is loaded by the MPEG_TABLE_SELECT Token and isreset to zero by the SEQUENCE_START Token.

[2519] B.8.8.4 Iq_ipeg_indirection[7:0]

[2520] This eight bit register determines which of the four quantizationtables will be used for each of the four possible color components thatoccur in a JPEG scan.

[2521] Bits [1.0] hold the table number that will be used for componentzero.

[2522] Bits [3.2] hold the able number that will be used for componentone.

[2523] Bits [5.4] hold the table number that will be used for componenttwo.

[2524] Bits [7.6] hold the table number that will be used for componentthree.

[2525] This register is affected by the JPEG_TABLE_SELECT Token.

[2526] B.8.8.5 iqquant scale[4.0]

[2527] This register holds the current value of the quantization scalefactor. This register is loaded by the QUANT_SCALE Token.

[2528] B.8.8.6 iq_component[1:0]

[2529] This register usually holds a value which is translated into theQuantization Table Matrix (QTM) number. It is loaded by a number ofTokens.

[2530] The DATA Token header causes this register be loaded with thecolor component of the block which is about to be processed. Thisinformation is only used in JPEG and JPEG variations to determine theQTM number, which it does with reference to iq_ipeg_indirection[7:0]. Inother standards, iq_component[1:0] is ignored.

[2531] The JPEG_TABLE_SELECT Token causes this register be loaded with acolor component. It is then used as an index intoiq_ipeg_indirection[7:0] which is accessed by the tokens body.

[2532] The QUANT_SCALE Token causes this register to be loaded with theQTM number. This table is then either loaded from the Token (if theextended form of the Token is used) or read out from the table to form aproperly extended Token.

[2533] B.8.8.7 iq_prediction_mode[1:0]

[2534] This two bit register holds the prediction mode that will be usedfor subsequent blocks. The only use that the Inverse Quantizer makes ofthis information is to decide whether or not intra coding is being used.If both bits of the register are zero, then subsequent blocks are intracoded.

[2535] This register is loaded by the PREDICTION_MODE Token. Thisregister is reset to zero by the SEQUENCE_START Token.

[2536] Iq_prediction_mode[1:0] has no effect on the operation in JPEGand JPEG variation modes.

[2537] B.8.8.8 Iq_ipeg_indirection[7:0]

[2538] Iq_ipeg_indirection is used as a lookup table to translate colorcomponents into the QTM number. Accordingly, iqcomponent is used as anindex to iq_ipeg_indirection as shown in Table B.8.3.

[2539] This register location is written to directly by theJPEG_TABLE_SELECT Token if the extended form of the Token is used.

[2540] This register location is read directly by the JPEG_TABLE_SELECTToken if the non-extended form of the Token is used.

[2541] B.8.8.9 Iq_quant_table[3:0][63:0][7:0]

[2542] There are four quantization tables, each with 64 locations. Eachlocation is an eight bit value. The value zero should not be used in anylocation.

[2543] These registers are implemented as a RAM described in B.8.6.3,“Igram”.

[2544] These tables may be loaded using the QUANT_TABLE Token.

[2545] Note that data in these tables are stored in zig-zag scan order.Many documents represent quantization table values as a square eight byeight array of numbers. Usually, the DC term is at the top left withincreasing horizontal frequency running left to right and increasingvertical frequency running top to bottom. Such tables must be read alongthe zig-zag scan path as the numbers are placed into the quantizationtable with consecutive “i”.

[2546] B.8.9 Microprocessor Register Map TABLE B.8.5 Memory Map RegisterLocation Direction Reset State iq_access 0x30 R/W 0 iq_coding_standard[1:0] 0x31 R/W 0 iq_quant_scale [4:0] 0x32 R/W ? iq_component [1:0] 0x33R/W ? iq_prediction_mode [1:0] 0x34 R/W 0 iq_ipeg_indirection [7:0] 0x35R/W ? iq_mpeg_indirection [1:0] 0x36 R/W 0 iq_qtm_keyhole_addr [7:0]0x38 R/W 0 iq_qtm_keyhole [7:0] 0x39 R/W ?

[2547] B.8.10 Test

[2548] Test coverage to the Inverse Quantizer at the input is throughthe Inverse Modeler's output snooper, and at the output through theInverse Quantizer's own snooper. Logic is covered by the InverseQuantizer's own scan chain.

[2549] Access can be gained to igram without reference to iq_access ifthe ramtest signal is asserted.

[2550] SECTION B.9 IDCT

[2551] B.9.1 Introduction

[2552] The purpose of this description of the Inverse Discrete CosineTransform (IDCT) block is to provide a source of engineering informationfor the IDCT. It includes information on the following.

[2553] purpose and main features of the IDCT

[2554] how it was designed and verified structure

[2555] It is intended that the description should provide one ofordinary skill in the art sufficient information to facilitate or aidthe following tasks.

[2556] appreciation of the IDCT as a “sillicon macro function”

[2557] integration the IDCT onto another device

[2558] development of test programs for the IDCT silicon

[2559] modification, re-design or maintenance of the IDCT

[2560] development of a forward DCT block

[2561] B.9.2 Overview

[2562] A Discrete Cosine Transform/Zig-Zag (DCT/ZZ) performs atransformation on blocks of pixels wherein each block represents an areaof the screen 8 pixels high by 8 pixels wide. The purpose of thetransform is to represent the pixel block in a frequence domain, sortedaccording to frequency. Since the eye is sensitive to DC components in apicture, but much less sensitive to high frequency components, thefrequency data allows each component to be reduced in magnitudeseparately, according to the eye's sensitivity. The process of magnitudereduction is known as quantization. The quantization process reduces theinformation contained in the picture, that is, the quantization processis lossy. Lossy processes give overall data compression by eliminatingsome information. The frequency data is sorted so that high frequencies,most likely to be quantized to zero, all appear consecutively. Theconsecutive zeros means that coding the quantized data by usingrun-length coding schemes yields further data compression, althoughrun-length coding is generally not a lossy process.

[2563] The IDCT block (which actually includes an Inverse Zig-Zag RAM,or IZZ, and an IDCT) takes frequency data, which is sorted, andtransforms it into spatial data. This inverse sorting process is thefunction of IZZ.

[2564] The picture decompression system, of which the IDCT block forms apart, specifies the pixels as integers. This means that the IDCT blockmust take, and yield, integer values. However, since the IDCT functionis not integer based, the internal number representation uses fractionalparts to maintain internal accuracy. Full floating-point arithmetic ispreferable, but the implementation described herein uses fixed-pointarithmetic. There is some loss of accuracy using fixed-point arithmetic,but the accuracy of this implementation exceeds the accuracy specifiedby H.261 and the IEEE.

[2565] B.9.3 Design Objectives

[2566] The main design objective, in accordance with the presentinvention, was to design a functionally correct IDCT block which uses aminimum silicon area. The design was also required to run with a clockspeed of 30 MHz under the specified operating conditions, but it wasconsidered that the design should also be adaptable for the future.Higher clock rates will be needed in the future, and the architecture ofthe design allows for this wherever possible.

[2567] B.9.4 IDCT Interfaces Description

[2568] The IDCT block has the following interfaces.

[2569] a 12-bit wide Token data input port

[2570] a 9-bit wide Token data output port

[2571] a microprocessor interface port

[2572] a system services input port

[2573] a test interface

[2574] resynchronizing signals

[2575] Both the Token data ports are the standard Two-Wire Interfacetype previously described. The widths illustrated, refer to the numberof bits in the data representation, not the total number of wires in aport. In addition, associated with the input Token data port are theclock and reset signals used for resynchronization to the output of theprevious block. There are also two resynchronizing clocks associatedwith the output Token data port and used by the subsequent block.

[2576] The microprocessor interface is standard and uses four bits ofaddress. There are also three externally decoded select inputs which areused to select the address spaces for events, internal registers andtest registers. This mechanism provides the flexibility to map the IDCTaddress space into different positions in different chips. There is alsoa single event output, idctevent, and two i/o signals, n_derrd andn_serrd, which are the event tristate data wires to be connectedexternally to the IDCT and to the appropriate bits of the microprocessornotdata bus.

[2577] The system services port consists of the standard clock and resetinput signals, as well as, the 2-phase override clocks and associatedclock override mode select input.

[2578] The test interface consists of the JTAG clock and reset signals,the scan-path data and control signals and the ramtest and chiptestinputs.

[2579] In normal operation, the microprocessor port is inactive sincethe IDCT does not require any microprocessor access to achieve itsspecified function. Similarly, the test interface is only active whentesting or verification is required.

[2580] B.9.5 The Mathematical Basis for the Discrete CosineTransformation

[2581] In video bandwidth compression, the input data represents asquare area of the picture. The transform applied must, therefore, betwo-dimensional. Two-dimensional transforms are difficult to computeefficiently, but the two-dimensional DCT has the property of beingseparable. Separable transforms can be computed along each dimensionindependent of the other dimensions. This implementation uses aone-dimensional IDCT algorithm designed specifically for mapping ontohardware; the algorithm is not appropriate for software models. Theone-dimensional algorithm is applied successively to obtain atwo-dimensional result.

[2582] The mathematical definition of the two-dimensional DCT for an Nby N block of pixels is as follows:

[2583] EQ 10. forward DCT${Y( {j,k} )} = {\frac{2}{N}{c(j)}{c(k)}{\sum\limits_{m = 0}^{N - 1}\quad {\sum\limits_{n = 0}^{N - 1}\quad {{X( {m,n} )}{\cos \lbrack \frac{( {{2m} + 1} )j\quad \pi}{2N} \rbrack}{\cos \lbrack \frac{( {{2n} + 1} )k\quad \pi}{2N} \rbrack}}}}}$

[2584] EQ 11. inverse DCT${X( {m,n} )} = {\frac{2}{N}{\sum\limits_{j = 0}^{N - 1}\quad {\sum\limits_{k = 0}^{N - 1}{c(j){c(k)}{Y( {j,k} )}{\cos \lbrack \frac{( {{2m} + 1} )j\quad \pi}{2N} \rbrack}{\cos \lbrack \frac{( {{2n} + 1} )k\quad \pi}{2N} \rbrack}}}}}$

[2585] Where $\begin{matrix}{j,{k = 0},1,\ldots,{N - 1}} \\{{{c(j)}{c(k)}} = ( \begin{matrix}\frac{1}{\sqrt{2}} & {j,{k = 0}} \\1 & {otherwise}\end{matrix} }\end{matrix}$

[2586] The above definition is mathematically equivalent to multiplyingtwo N by N matrices, twice in succession, with a matrix transpositionbetween the multiplications. A one-dimensional DCT is mathematicallyequivalent to multiplying two N by N matrices. Mathematically thetwo-dimensional case is:

Y=[XC]^(T)C

[2587] Where C is the matrix of cosine terms.

[2588] Thus the DCT is sometimes described in terms of matrixmanipulation. Matrix descriptions can be convenient for mathematicalreductions of the transform, but it must be stressed that this onlymakes notation easier. Note that the 2/N term governs the DC level. Theconstants c(j) and c(k) are known as the normalization factors.

[2589] B.9.6 The IDCT Transform Algorithm

[2590] As subsequently explained in further detail, the algorithm usedto compute the actual IDCT transform should be a “fast” algorithm. Thealgorithm used is optimized for an efficient hardware architecture andimplementation. The main features of the algorithm are the use of{square root}2 scaling in order to remove one multiplication, and atransformation of the algorithm designed to yield a greater symmetrybetween the upper and lower sections. This symmetry results in anefficient re-use of many of the most costly arithmetic elements.

[2591] In the diagram illustrating the algorithm (FIG. 136), thesymmetry between the upper and lower halves is evident in the middlesection. The final column of adders and subtractors also has a symmetry,the adders and subtractors can be combined with relatively little cost(4 adder/subtractors being significantly smaller than 4 adders+4subtractors as illustrated).

[2592] Note that all the outputs of a single dimensional transform arescaled by V2. This means that the final 2-dimensional answer will bescaled by 2. This can then be easily corrected in the final saturationand rounding stage by shifting.

[2593] The algorithm shown was coded in double precision floating-pointC and the results of this compared with a reference IDCT (usingstraightforward matrix multiplication). A further stage was then used tocode a bit-accurate integer version of the algorithm in C (no timinginformation was included) which could be used to verify the performanceand accuracy of the algorithm as it would be implemented on silicon. Theallowable inaccuracies of the transform are specified in the H.261standard and this method was used to exercise the bit-accurate model andmeasure the delivered accuracy.

[2594]FIG. 137 shows the overall IDCT Architecture in a way thatillustrates the commonality between the upper and lower sections andwhich also shows the points at which intermediate results need to bestored. The circuit is time multiplexed to allow the upper and lowersections to be calculated separately.

[2595] B.9.7 The IDCT Transform Architecture

[2596] As described previously, the IDCT algorithm is optimized for anefficient architecture. The key features of the resulting architectureare as follows:

[2597] significant re-use of the costly arithmetic operations

[2598] small number of multipliers, all being constant coefficientrather than general purpose (reduces multiplier size and removes needfor separate coefficient store)

[2599] small number of latches, no more than required for pipelining thearchitecture

[2600] operations are arranged so that only a single resolving operationis required per pipeline stage

[2601] can arrange to generate results in natural order

[2602] no complex crossbar switching or significant multiplexing (bothcostly in a final implementation)

[2603] advantage is taken of resolved results in order to remove twocarry-save operations (one addition, one subtraction)

[2604] architecture allows each stage to take 4 clock cycles, i.e.,removes the requirement for very fast (large) arithmetic operations

[2605] architecture will support much faster operation than current 30MHz pixel-clock operation by simply changing resolving operations fromsmall/slow ripple carry to larger/faster carry-lookahead versions. Theresolving operations require the largest proportion of the time requiredin each stage so speeding up only these operations has a significanteffect on the overall operations speed, whilst having only a relativelysmall increase on the overall size of the transform. Further increasesin speed can also be achieved by increasing the depth of pipelining.

[2606] control of the transform data-flow is very straightforward andefficient

[2607] The diagram of the 1D Transform Micro-Architecture (FIG. 141)illustrates how the algorithm is mapped onto a small set of hardwareresources and then pipelined to allow the necessary performanceconstraints to be met. The control of this architecture is achieved bymatching a “control shift-register” to the data-flow pipeline. Thiscontrol is straightforward to design and is efficient in silicon layout.

[2608] The named control signals on FIG. 141 (latch,selbyp etc.) are thevarious enable signals used to control the latches and, thus, the signalflow. The clock signals to the latches are not shown.

[2609] Several implementation details are significant in terms ofallowing the transform architecture to meet the required accuracystandards whilst minimizing the transform size. The techniques usedgenerally fall into two major classes.

[2610] Retention of maximum dynamic range, with a fixed word width, ateach intermediate state by individual control of the fixed-pointposition.

[2611] Making use of statistical definition of the accuracy requirementin order to achieve accuracy by selective manipulation of arithmeticoperations (rather than increasing accuracy by simply increasing theword width of the entire transform)

[2612] The straightforward way to design a transform would involve asimple fixed-point implementation with a fixed word-width made largeenough to achieve accuracy. Unfortunately, this approach results in muchlarger word widths and, therefore, a larger transform. The approach usedin the present invention allows the fixed point position to varythroughout the transform in a manner that makes the maximum use of theavailable dynamic range for any particular intermediate value, achievingthe maximum possible accuracy.

[2613] Because the allowable results are specified statistically,selective adjustments can be made to any intermediate value truncationoperation in order to improve overall accuracy. The adjustments chosenare simple manipulations of LSB calculations, which have little or nocost. The alternative to this technique is to increase the word width,involving significant cost. The adjustments effectively “weight” finalresults in a given direction, if it is found that previously, theseresults tend in the opposite direction. By adjusting the fractionalparts of results, we are effectively shifting the overall average ofthese results.

[2614] B.9.8 IDCT Block Diagram Description

[2615] The block diagram of the IDCT shows all the blocks that arerelevant to the processing of the Token Stream. This diagram, FIG. 138,does not show details of clocking, test and microprocessor access andthe event mechanism. snooper blocks, used to provide test access, arenot shown in the diagram.

[2616] B.9.8.1 DATA Error Checker

[2617] The first block is the DATA error checker and corrector, called“decheck” which takes and produces a 12-bit wide Token Stream, parsesthis stream and checks the DATA Tokens. All other Tokens are ignored andare passed straight through. The checks that are performed are for DATATokens with a number of extensions not equal to 64. The possible errorsare termed “deficient” (<64 extensions) an idct_too_few_event, and“supernumerary” (>64 extensions), an idct_too_many_event. Such errorsare signalled with the standard event mechanism, but the block alsoattempts simple error recovery by manipulation of the Token Stream. Inthe case of deficient errors, the DATA Token is packed with “0” valueextensions (stops accepting input and performs insert) to make up thecorrect 64 extensions. In the case of a supernumerary error, theextension bit is forced to “0” for the 64th extension and all extraextensions are removed from the Token Stream.

[2618] B.9.8.2 Inverse Zig-zag

[2619] The next block on the Spatial Decoder in FIG. 138 is the inversezig-zag RAM 441, “izz”, and again it takes and produces a 12-bit wideToken Stream. As with all other blocks, the stream is parsed, but onlyDATA Tokens are recognized. All other Tokens are passed throughunchanged. DATA Tokens are also passed through, but the order of theextensions is changed. This block relies on correct DATA Tokens (i.e.,64 extensions only). If this is not true, then operation is unspecified.The reordering is done according to the standard inverse Zig-Zag patternand, by default, is done so as to provide horizontally scanned data atthe IDCT output. It is also possible to change the ordering to providevertically scanned output. In addition to the standard IZZ ordering,this block performs an extra re-ordering of each 8-word row. This isdone because of the specific requirements of the IDCT one-dimensionaltransform block and results in rows being output in the order(1,3,5,7,0,2,4,6) rather than (0,1,2,3,4,5,6,7).

[2620] B.9.8.3 Input Formatter

[2621] The next block in FIG. 138 is the input formatter 442, “ip_fmt”,which formats DATA input for the first dimension of the IDCT transform.This block has a 12-bit wide Token Stream input and 22-bit wide tokenStream output. DATA Tokens are shifted left so as to move the integerpart to the correct significance in the IDCT transform standard 22-bitwide word, the fractional part being set to 0. This means that there are10 bits of fraction at this point. All other Tokens are unshifted andthe extra unused bits are simply set to 0.

[2622] B.9.8.4 1-Dimensional Transform—1st Dimension

[2623] The next block shown in FIG. 138 is the first single dimensionIDCT transform block 443, “oned”. This inputs and outputs 22-bit widetoken Streams and, as usual, the stream is parsed and DATA Tokens arerecognized. All other tokens are passed through unaltered. The DATATokens pass through a pipelined datapath that performs an implementationof a single dimension of an 8-by-8 Inverse Discrete Cosine Transform. Atthe output of the first dimension, there are 7 bits of fraction in thedata word. All other Tokens run through a merely shift register datapaththat simply matches the DATA transform latency and are recombined intothe Token Stream before output.

[2624] B.9.8.5 Transpose RAM

[2625] The transpose RAM 444 “tram”, is similar in many ways to theinverse zig-zag RAM 441 in the way it handles a Token Stream. The widthof Tokens handled (22 bits) and the re-ordering performed are different,but otherwise they work in the same way and actually share much of theircontrol logic. Again, rows are additionally re-ordered for therequirements of the following IDCT dimension as well as the fundamentalswapping of columns into rows.

[2626] B.9.8.6 1-Dimensional Transform—2nd Dimension

[2627] The next block shown is another instance of a single dimensionIDCT transform and is identical in every way to the first dimension. Atthe output of this dimension there are 4 bits of fraction.

[2628] B.9.8.7 Round and Saturate

[2629] The round-and-saturate block 446 in FIG. 138, “ras”, takes a22-bit wide Token Stream containing DATA extensions in 22-bit fixedpoint format and outputs a 9-bit wide Token Stream where DATA extensionshave been rounded (towards +ve infinity) into integers and saturatedinto 9-bit two's complement representation and all other Tokens havebeen passed straight through.

[2630] B.9.9 Hardvare Descriptions of Blocks

[2631] B.9.9.1 Standard Block Structure

[2632] For all the blocks that handle a Token Stream there is a standardnotional structure as shown in FIG. 139. This separates the two-wireinterface latches from the section that performs manipulation of theToken Stream. Variations on this structure can include extra internalblocks (such as a RAM core). In some blocks shown, the structure is madeless obvious in the schematic (although it does actually still exist)because of the requirement of grouping together all the “datapath” logicand separate this from all the standard cell logic. In the case of avery simple block, such as “ras”, it is possible to take the latched outaccept straight into the input two-wire latch without logicalmanipulation.

[2633] B.9.9.2 “Decheck”—DATA Error Chocking/Recovery

[2634] The first block 440 in the Token Stream performs DATA checkingand correcting as specified in the Block Diagram Overview section. Thedetected errors are handled with the standard event mechanism whichmeans that events can be masked and the block can either continue withthe recovery procedure when an error is detected or be stopped dependingon event mask status. The IDCT should never see incorrect DATA Tokensand, therefore, the recovery that it attempted is only a fairly simpleattempt to contain what may be a serious problem.

[2635] This block has a pipeline depth of two stages and is implementedentirely in zcells. The input two-wire interface latch is of the “front”type, meaning that all inputs arrive onto transistor gates to allow safeoperation when this block (at the front of the IDCT) is on a separatepower supply regime from the one preceding it. This block works byparsing a Token Stream and passing non-DATA Tokens straight through.When a DATA Token is found, a count is started of the number ofextensions found after the header. If the extension bit is found to be“0” when the count does not equal 63, an error signal is generated(which goes to the event logic) and depending on the state of the maskbit for that event, “decheck” will either be stopped (i.e., no longeraccept input or generate output) or will begin error recovery. Therecovery mechanism for “deficient” errors uses the counter to controlthe insertion of the correct number of extensions into the Token Stream(the value inserted is always “0”). Obviously, input is not acceptedwhilst this insertion proceeds. When it is found that the extension bitis not “0” on the 64th extension, a “supernumerary” error is generated,the DATA Token is completed by forcing the extension bit to “0”, and allsucceeding words with the extension bit set to “1” are deleted from theToken Stream by continuing to accept data but invalidating the output.

[2636] Note that the two error signals are not persistent (unless theblock is stopped) i.e., the error signal only remains active from thepoint when an error is detected until recovery is complete. This is aminimum of one complete cycle and can persist forever in the case of ainfinitely supernumerary DATA Token.

[2637] B.9.9.3 “Izz” and “tram”—Reordering RAMs

[2638] The “izz” 441 (inverse zig-zag RAM) and the “tram” 444 (transposeRAM) are considered here together since they both perform a variation onthe same function and they have more similarities than differences. Boththese blocks take a Token Stream and re-order the extensions of a DATAToken whilst passing through all other Tokens unchanged. The widths ofthe extensions handled and the sequences of the re-ordering aredifferent, but a large section of the control logic for each RAM isidentical and is actually organized into a “common control” block whichis instanced in the schematic for each RAM. The difference in width hasno effect upon this control section so it is only necessary to use adifferent “sequence address generator” for each RAM together with RAMcores and two-wire interface blocks of the appropriate width.

[2639] The overall behavior of each RAM is essentially that of a FIFO.This is strictly true at the Token level and a particular modificationto the output order is made for the extension words of a DATA Token. Thedepth of the FIFO is 128 stages. This is necessary to fulfill therequirement for a sustainable 30 MHz throughout the system since outputof the FIFO is held up after the start of the output of a DATA Token isdetected. This is because the features of the reordering sequences usedrequire that a complete block of 64 extensions be gathered in the FIFObefore re-ordered output can begin. More precisely, the minimum numberrequired is different for inverse zig-zag and transpose sequences and issomewhat less than 64 in both cases. However, the complications ofcontrolling a FIFO which has a length which is not a power of two, meansthat the small saving in RAM core would be outweighed by the additionalcomplexity of control logic required.

[2640] The RAM core is implemented with a design which allows a read anda write (to the same or separate addresses) in a single 30 MHz cycle.This means that the RAM is effectively operating with an internal 60 MHzcycle time.

[2641] The re-ordering operation is performed by generating a particularsequence of read addresses (“sequence address generation”) in the range0->63, but not in natural order. The sequences required are specified bythe standard zig-zag sequence (for eight horizontal or verticalscanning) or by the sequence needed for normal matrix transposition.These standard sequences are then further reordered by the requirementto output each row in Odd/Even format (i.e., 1,3,5,7,0,2,4,6) ratherthan (0,1,2,3,4,5,6,7)) because of the requirements of the IDCTtransform 1-dimensional blocks.

[2642] Transpose address sequence generation is quite straightforwardalgorithmically. Straight transpose sequence generation simply requiresthe generation of row and column addresses separately, both implementedwith counters. The row re-ordering requirement simply means that rowaddresses are generated with a simple specific state machine rather thana natural counter.

[2643] Inverse zig-zag sequences are rather less straightforward togenerate algorithmically. Because of this fact, a small ROM is used tohold the entire 64 6 bit values of address, this being addressed withrow and column counters which can be swapped in order to change betweenhorizontal and vertical scan modes. A ROM based generator is very quickto design and it further has the advantage that it is trivial toimplement a forward zig-zag (ROM re-program) or to add other alternativesequences in the future.

[2644] B.9.9.4 “Oned”—Single Dimension IDCT Transform

[2645] This block has a pipeline depth of 20 stages and the pipeline isrigid when stalled. This rigidity greatly simplifies the design andshould not unduly affect overall dynamics since the pipeline depth isnot that great and both dimensions come after a RAM which provides acertain amount of buffering.

[2646] The block follows the standard structure, but has separate pathsinternally for DATA Token extensions (which are to be processed) and allother items which should be passed through unchanged. Note that theschematic is drawn in a particular way. First, because of therequirements to group together all the datapath logic and second, toallow automatic compiled code generation (this explains the controllogic at the top level).

[2647] Tokens are parsed as normal and then DATA extensions, and othervalues, are routed respectively through two different parallel pathsbefore being re-combined with a multiplexer before the output two-wireinterface latch block. The parallel paths are required because it is notpossible to pass values unchanged through the transform datapath. Thelatency of the transform datapath is matched with a simple shiftregister to handle the remainder of the Token Stream.

[2648] The control section of “oned” needs to parse the Token Stream andcontrol the splitting and re-combination of the Tokens. The other majorsection controls the transform datapath. The main mechanism for thecontrol of this datapath is a control shift-register which matches thedatapath pipeline and is tapped-off to provide the necessary controlsignals for each stage of the datapath pipeline.

[2649] The “oned” block has the requirement that it can only startoperation on complete rows of DATA extensions, i.e., groups of 8. It isnot able to handle invalid data (“Gaps”) in the middle of rows,although, in fact, the operation of “izz” and the “tram” ensure thatcomplete DATA blocks are output as an uninterrupted sequence of 64 validextension values.

[2650] B.9.9.4.1 Transform DataPath

[2651] The micro-architecture of the transform datapath, “t_dp” waspreviously shown in FIG. 141. Note that some detail (e.g., clocking,shifts, etc.) is not shown. This diagram does illustrate, however, howthe datapath operates on four values simultaneously at any stage in thepipeline. The basic sub-Structure of the datapath, i.e., the three mainsections can also be seen (e.g., pre-common, common and post-common) ascan the arithmetic and latch resources required. The named controlsignals are the enables for the-pipeline latches (and the add/subselector) which are sequenced with decodes of the control shift-registerstate. Note that each pipeline stage is actually four clock cycles inlength.

[2652] Within the transform datapath there are a number of latch stageswhich are required to gather input, store intermediate results in thepipeline, and serialize the output. Some of latches are of the muxingtype, i.e., they can be conditionally loaded from more than one source.All the latches are of the enabled type, i.e., there are separate clockand enable inputs. This means that it is easy to generate enable signalswith the correct timing, rather than having to consider issues of skewthat would arise if a generated clock scheme was adopted.

[2653] The main arithmetic elements required are as follows.

[2654] a number of fixed coefficient multipliers

[2655] (carry-save output)

[2656] carry-save adders

[2657] carry-save subtractors

[2658] resolving adders

[2659] resolving adder/subtractors

[2660] All arithmetic is performed in two's complement representation.This can either be in normal (resolved) form or in carry-save form(i.e., two numbers whose sum represents the actual value). All numbersare resolved before storage and only one resolving operation isperformed per pipeline stage since this is the most expensive operationin terms of time. The resolving operations performed here all use simpleripple-carry. This means that the resolvers are quite small, butrelatively slow. Since the resolutions dominate the total time in eachstage, there is obviously an opportunity to speed up the entiretransform by employing fast resolving arithmetic units.

[2661] B.9.9.5 “Ras”—Rounding and Saturation

[2662] In the present invention, the “ras” block has the task of taking22-bit fixed point numbers from the output of the second dimension“oned” and turning these into the correctly rounded and saturated 9-bitsigned integer results required. This block also performs the necessarydivide-by-4 inherent in the scheme (the 2/N term) and to furtherdivide-by-2 required to compensate for the {square root}2 pre-scalingperformed in each of the two dimensions. This division by 8 implies thatthe fixed point position is interpreted as being three bits further leftthan anticipated, i.e., treat the result as having 15 bits of integerrepresentation and 7 bits of fraction (rather than 4 bits of fraction).The rounding mode implemented is “round to positive infinity”, i.e., addone for fractions of exactly 0.5. This is primarily done because it isthe simplest rounding mode to implement. After rounding (a conditionalincrement of the integer part) is complete, this result is inspected tosee whether the 9-bit signed result requires saturation to the maximumor minimum value in this range. This is done by inspection of theincrement carry out together with the upper bits of the original integervalue.

[2663] As usual, the Token Stream is parsed and the round and saturationoperation is only applied to DATA Token extension values, The block hasa pipeline depth of two stages and is implemented entirely in zcells.

[2664] B.9.9.6 “Idctsels”—IDCT Register Select Decoder

[2665] This block is a simple decoder which decodes the 4 microprocessorinterface address lines, and the “sel_test” input, into select lines forindividual blocks test access (snoopers and RAMs). The block consistsonly of zcells combinatorial logic. The selects decoded are shown inTable B.9.2. TABLE B.9.1 IDCT Test Address Space Addr. Bit (hex) num.Register Name 0x0 7..1 not used 0 TRAM keyhole address 0x1 7..0 0x2 7..0TRAM keyhole data 0x3 7..0 TRAM keyhole data^(a) 0X4 7..0 IZZ keyholeaddress 0x5 7..0 IZZ keyhole data 0x6 7..3 not used 2 ipfsnoop testselect 1 ipfsnoop valid 0 ipfsnoop accept 0x7 7..6 not used 5..0ipfsnoop bits[21:16] 0x8 7..0 ipfsnoop bits[15:8] 0x9 7..0 ipfsnoopbits[7:0] 0xA 7..3 not used 2 d2snoop test select 1 d2snoop valid 0d2snoop accept 0xB 7..6 not used 5..0 d2snoop bits[21:16] 0xC 7..0d2snoop bits[15:8] 0xD 7..0 d2snoop bits[7:0] 0xE 7 outsnoop test select6 outsnoop valid 5 outsnoop accept 4..2 not used 0xE 1..0 outsnoopdata[9:8] 0xF 7..0 outsnoop data[7:0]

[2666] B.9.9.7 “Idctregs”—IDCT Control Register and Events

[2667] This block of the invention contains instances of the standardevent logic blocks to handle the DATA deficient and supernumerary errorsand also a single memory mapped bit “vscan” which can be used to makethe “izz” re-ordering change such that the IDCT output is verticallyscanned. This bit is reset to the value “0”, i.e., the default mode ishorizontally scanned output. The two possible events are OR-ed togetherto form an idctevent signal which can be used as an interrupt. SeeSection B.9.10 for the addresses and bit positions of registers andevents.

[2668] B.9.9.8 Clock Generators

[2669] Two “standard” type (“clkgen”) clock generators are used in theIDCT. This is done so that there can be two separate scan-paths. Theclock generators are called “idctcga” and “idctcgb”. Functionally, theonly difference is that “idctcgb” does not need to generate the“notrstl” signal. The amounts of buffering for each of the clock andreset outputs in the two clock generators is individually tailored tothe actual loads driven by each clock or reset. The loads that arematched were actually measured from the gate and track capacitances ofthe final layout.

[2670] When the IDCT top-level Block Place and Route (BPR) wasperformed, advantage was taken of the capabilities of the interactiveglobal routing feature to increase the widths of tracks of the firstsections of the clock distribution trees for the more heavily loadedclocks (ph0_b and ph1_b) since these tracks will carry significantcurrents.

[2671] B.9.9.9 JTAG Control Blocks

[2672] Since the IDCT has two separate scan-chains, and two clockgenerators, there are two instances of the standard JTAG control block,“jspctle”. These interface between the test port and the two scan-paths.

[2673] B.9.10 Event and Control Registers

[2674] The IDCT can generate two events and has a single bit of control.The two events are idcttoofewevent and idct too many event which can begenerated by the “decheck”block at the front of the IDCT if incorrectDATA Tokens are detected. The single control bit is “vscan” which is setif it is required to operate the IDCT with the output verticallyscanned. This bit, therefore, controls the “izz” block. All the eventlogic and the memory mapped control bit are located in the block“idctregs”.

[2675] From the point of view of the IDCT, these registers are locatedin the following locations. The tristate i/o wires n_derrd and n-serrdare used to read and write to these locations as appropriate. TABLEB.9.2 IDCT Control Register Address Space Addr. Bit (hex) num. RegisterName 0x0 7..1 not used 0 vscan

[2676] TABLE B.9.3 IDCT Event Address Space Addr. Bit (hex) nameRegister Name 0x0 n_derrd idct_too_few_event n_serrd idct_too_many_event0x1 n_derrd idct_too_few_mask n_serrd idct_too_many_mask

[2677] B.9.11 Implementation Issues

[2678] B.9.11.1 Logic Design Approach

[2679] In the design of all the IDCT blocks, in accordance with theinvention, there was an attempt to use a unified and simple logic designstrategy which would mean that it was possible to do a “safe” design ina quick and straightforward manner. For the majority of control logic, asimple scheme of using master-slaves only was adopted. Asynchronousset/reset inputs were only connected to the correct system resets.Although it might often be possible to come up with clever non-standardcircuit configurations to perform the same functions more efficiently,this scheme possesses the following advantages.

[2680] conceptually simple

[2681] easy to design

[2682] speed of operation is fairly obvious (cf. latch→logic→latch>logicstyle design) and amenable to automatic analysis

[2683] glitches not a problem (cf. SR latches)

[2684] using only system reset for initialization allows scan paths towork correctly

[2685] allows automatic complied C-code generation

[2686] There are a number of places where transparent d-type latcheswere used and these are listed below.

[2687] B.9.11.1.1 Two-wire Interface Latches

[2688] The standard block structure uses latches for the input andoutput two-wire interfaces. No logic exists between an output two-wirelatch and the following input two-wire latch.

[2689] B.9.11.1.2 ROM Interface

[2690] Because of the timing requirements of the ROM circuit, latchesare used in the IZZ sequence generator at the output of the ROM.

[2691] B.9.11.1.3 Transform Datapath and Control Shift-Register

[2692] It is possible to implement every pipeline storage stage as afull master-slave device, but because of the amount of storage requiredthere is a significant savings to be had by using latches. However, thisscheme requires the user to consider several factors.

[2693] control shift-register must now produce control signals of bothphases for use as enables (i.e., need to use latches in thisshift-register)

[2694] timing analysis complicated by use of latches

[2695] the “t_postc” will no longer automatically produce compiled codesince one latch outputs to another latch of the same phase (because ofthe timing of the enables this is not a problem for the circuit)

[2696] Nonetheless, the area saved by the use of latches makes itworthwhile to accept these factors in the present invention.

[2697] B.9.11.1.4 Microprocessor Interfaces

[2698] Due to the nature of this interface, there is a requirement forlatches (and resynchronizers) in the Event and register block “idctregs”and in the keyhole logic for RAM cores.

[2699] B.9.11.1.5 JTAG Test Control

[2700] These standard blocks make use of latches.

[2701] B.9.11.2 Circuit Design Issues

[2702] Apart from the work done in the design of the library cells thatwere used in the IDCT design (standard cells, datapath library, RAMs,ROMs, etc.) there is no requirement for any transistor level circuitdesign in the IDCT. Circuit simulations (using Hspice) were performed ofsome of the known critical paths in the transform datapath and Hspicewas also used to verify the results of the Critical Path Analysis (CPA)tool in the case of paths that were close to the allowed maximum length.

[2703] Note that the IDCT is fully static in normal operation (i.e., wecan stop the system clocks indefinitely) but there are dynamic nodes inscanable latches which will decay when test clocks are stopped (or veryslow). Due to the non-restored nature of some nodes which exhibit a Vtdrop (e.g., mux outputs) the IDCT will not be “micro-power” when static.

[2704] B.9.11.3 Layout Approach

[2705] The overall approach to the layout implementation of the presentinvention was to use BPR (some manual intervention) to lay out acomplete IDCT which consisted of many zcells and a small number of macroblocks. These macro blocks were either hand-edited layout (e.g., RAMs,ROM, clock generators, datapaths) or, in the case of the “oned” block,had been built using BPR from further zcells and datapaths.

[2706] Datapaths were constructed from kdplib cells. Additionally,locally defined layout variations of kdplib cells were defined and usedwhere this was perceived as providing a worthwhile size benefit. Thedatapath used in each of the “oned” blocks, “oned_d”, is by far thelargest single element in the design and considerable effort was putinto optimizing the size (height) of this datapath. The organization ofthe transform datapath, “t_dp”, is rather crucial since the preciseordering of the elements within the datapath will affect the way theinterconnect is handled. It is important to minimize the number of“overs” (vertical wires not connecting to a sub-block) which occur atthe most congested point since there is a maximum allowed value (ideally8, 10 is also possible, although highly inconvenient). The datapath issplit logically into three major sub-sections and this is the way thatthe datapath layout was performed. In each subsection, there are reallyfour parallel data flows (which are combined at various points) andthere are, therefore, many ways of organizing the flows of data (and,thus, the positions of all the elements) within each subsection. Theordering of the blocks within each subsection, and also the allocationof logical buses to physical bus pitches was worked out carefully beforelayout commenced in order to make it possible to achieve a layout thatcould be connected correctly.

[2707] B.9.12 Verification

[2708] The verification of the IDCT was done at a number of levels, fromtop-level verification of the algorithms to final layout checks.

[2709] The initial work on the transform architecture was done in C,both full-precision and bit-accurate integer models were developed.Various tests were performed on the bit-accurate model in order to provethe conformance to the H.261 accuracy specification and to measure thedynamic ranges of the calculations within the transform architecture.

[2710] The design progressed in many cases by writing an M behavioraldescription of sub-blocks (for example, the control of datapaths andRAMs). Such descriptions were simulated in Lsim before moving onto thedesign of the schematic description of that block. In some cases (e.g.,RAMs, clock generators) the behavioral descriptions were still used fortop-level simulations.

[2711] The strategy for performing logic simulation was to simulate theschematics for everything that would simulate adequately at that level.The low-level library cells (i.e., zcells and kdplib) were mainlysimulated using their behavioral descriptions since this results in farsmaller and quicker simulations. Additionally, the behavioral librarycells provide timing check features which can highlight some circuitconfiguration problems. As a confidence check, some simulations wereperformed using the transistor descriptions of the library cells. Allthe logic simulations were in the zero-delay manner and, therefore, wereintended to verify functional performance. The verification of the realtiming behavior is done with other techniques.

[2712] Lsim switch-level simulations (with RC_Timing mode being used)were done as a partial verification of timing performance, but alsoprovide checks for some other potential transistor level problems (e.g.,glitch sensitive circuits).

[2713] The main verification technique for checking timing problems wasthe use of the CPA tool, the “path” option for “datechk”. This was usedto identify the longer signal paths (some were already known) and Hspicewas used to verify the CPA analysis in some critical cases.

[2714] Most Lsim simulations were performed with the standardsource→block→sink methodology since the bulk of the IDCT behavior isexercised by the flow of Tokens through the device. Additionalsimulations are also necessary to test the features accessed through themicroprocessor interface (configuration, event and test logic) and thosetest features accessed via JTAG/scan.

[2715] Compiled-code simulations can be readily accomplished by one ofordinary skill in the art for entire IDCT, again using the standardsource→bloc→sink method and many of the same Token Streams that wereused in the Lsim verification.

[2716] B.9.13 Testing and Test Support

[2717] This section deals with the mechanisms which are provided fortesting and an analysis of how each of the blocks might be tested.

[2718] The three mechanisms provided for test access are as follows:

[2719] microprocessor access to RAM cores

[2720] microprocessor access to snooper blocks

[2721] scan path access to control and datapath logic

[2722] There are two “snooper” blocks and one “super snooper” block inthe IDCT. FIG. 140 shows the positions of the snooper blocks and theother microprocessor test access.

[2723] Using these, and the two RAM blocks, it is possible to isolateeach of the major blocks for the purpose of testing their behavior inrelation to the Token flow. Using microprocessor access, it is possibleto control the Token inputs to any block andc then to observe the Tokenport output of that block in isolation. Furthermore, there are twoseparate scan paths which run through (almost) all of the flip-flops andlatches in the control sections of each block and also some of thedatapath latches in the case of the “oned” transform datapath pipeline.The two scan paths are denoted “a” and “b”, the former running from the“decheck” block to the “ip_fmt” block and the latter from the first“oned” block to the “ras” block.

[2724] Access to snoopers is possible by accessing the appropriatememory mapped locations in the normal manner. The same is true of theRAM cores (using the “ramtest” input as appropriate). The scan paths areaccessed through the JTAG port in the normal way.

[2725] Each of the blocks is now discussed with reference to the varioustest issues.

[2726] B.9.13.1 “Decheck”

[2727] This block has the standard structure (see FIG. 139) where twolatches for the input and output two-wire interfaces surround aprocessing block. As usual, no scan is provided to the two-wire latchessince these simply pass on data whenever enabled and have no depth oflogic to be tested. In this block, the “control” section consists of a1-stage pipeline of zcells which are all on scanpath “a”. The logic inthe control section is relatively simple, the most complex path isprobably in the generation of the DATA extension count where a 6-bitincrementer is used.

[2728] B.9.13.2 “Izz”

[2729] This block is a variant of the standard structure and includes aRAM core block added to the two-wire interface latches and the controlsection. The control section is implemented with zcells and a small ROMused for address sequence generation. All the zcells are on scanpath “a”and there is access to the ROM address and data via zcell latches. Thereis also further logic, e.g., for the generation of numbers plus theability to increment or decrement. In addition, there is a 7-bit fulladder used for read address generation. The RAM core is accessiblethrough keyhole registers, via the microprocessor interface, see TableB.9.1.

[2730] B.9.13.3 “lp_fmt”

[2731] This block again has the standard structure. Control logic isimplemented with some rather simple zcell logic (all on scanpath “a”)but the latching and shifting/muxing of the data is performed in adatapath with no direct access since the logic here is very shallow andsimple.

[2732] B.9.13.4 “Oned”

[2733] Again, this block follows the standard structure and divides intorandom logic and datapath sections. The zcell logic is relativelystraightforward; all the zcells are on scanpath “a”. The control signalsfor the transform pipeline datapath are derived from a long shiftregister consisting of zcell latches which are on the scanpath.Additionally, some of the pipeline latches are on the scanpath, thisbeing done because there is a considerable depth of logic between somestages of the pipeline (e.g., multipliers and adders). The non-DATATokens are passed along a shift register, implemented as a datapath, andthere is no test access to any of the stages

[2734] B.9.13.5 Tram′

[2735] This block is very similar to the “izz” block. In this case,however, there is no ROM used in the address sequence addressgeneration. This is performed algorithmically. All the zcell controlstates are on datapath “b”.

[2736] B.9.13.6 Rras′

[2737] This block follows the standard structure and is entirelyimplemented with zcells. The most complex logical function is the 8-bitincrementer used when rounding up. All other logic is fairly simple. Allstates are scanpath “b”.

[2738] B.9.13.7 Other Top-level Blocks

[2739] There are several other blocks that appear at the top level ofthe IDCT. The snoopers are obviously part of the test access logic, asare the JTAG control blocks. There are also the two clock generatorswhich do not have any special test access (although they support varioustest features). The block “idctsels” is combinatorial zcell logic fordecoding microprocessor addresses and the block “idctregs” contains themicroprocessor accessible event and control bits associated with theIDCT.

[2740] SECTION B.10 Introduction

[2741] B.10.1 Overview of the Temporal Decoder

[2742] The internal structure of the Temporal Decoder, in accordancewith the invention, is shown in FIG. 142.

[2743] All data flow between the blocks of the chip (and much of thedata flow within blocks) is controlled by means of the usual two-wireinterfaces and each of the arrows in FIG. 142 represents a two-wireinterface. The incoming token stream passes through the input interface450 which synchronizes the data from the external system clock to theinternal clock derived from the phase-locked-loop (ph0/ph1). The tokenstream is then split into two paths via a Top Fork 451; one streampasses to the Address Generator 452 and the other to a 256 word FIFO453. The FIFO buffers data while data from previous I or P frames isfetched from the DRAM and processed in the Prediction Filters 454 beforebeing added to the incoming error data from the Spatial Decoder in thePrediction Adder 455 (P and B frames). During MPEG decoding, framereordering data must also be fetched for I and P frames so that theoutput frames are in the correct order, the reordered data beinginserted into the stream in the Read Rudder block 456.

[2744] The Address Generator 452 generates separate addresses forforward and backward predictions, reorder, read and write-back, the datawhich is written back being split from the stream in the Write Rudderblock 457. Finally, data is resynchronized to the external clock in theOutput Interface Block 458.

[2745] All the major blocks in the Temporal Decoder are connected to theinternal microprocessor interface (UPI) bus. This is derived from theexternal microprocessor interface (MPI) bus in the MicroprocessorInterface block 459. This block has address decodes for the variousblocks in the chip associated with it. Also associated with themicroprocessor interface is the event logic.

[2746] The rest of the logic of the Temporal Decoder is concernedprimarily with test. First, the IEE 1149.1 (JTAG) interface 460 providesan interface to internal scan paths as well as to JTAG boundary-scanfeatures. Secondly, two-wire interface stages which allow intrusiveaccess to the data flow via the microprocessor interface while in testmode are included at strategic points in the pipeline architecture.

[2747] SECTION B.11 Clocking, Test and Related Issues

[2748] B.11.1 Clock Regimes

[2749] Before considering the individual functional blocks within thechip, it is helpful to have an appreciation of the clock regimes withinthe chip and the relationship between them.

[2750] During normal operation, most blocks of the chip runsynchronously to the signal pllsysclk from the phase-locked-loop (PLL)block. The exception to this is the DRAM interface whose timing isgoverned by the need to be synchronous to the iftime sub-block, whichgenerates the DRAM control signals (notwe, notoe, notcas, notras). Thecore of this block is clocked by the two-phase non-overlapping clocksclk0 and clk1, which are derived from the quadrature two-phase clockssupplied independently from the PLL cki0, cki1 and clkq0, ckq1.

[2751] Because the clk0, clk1 DRAM interface clocks are asynchronous tothe clocks in the rest of the chip, measures have been taken toeliminate the possibility of metastable behavior (as far as practicallypossible) at the interfaces between the DRAM interface and the rest ofthe chip. The synchronization occurs in two areas: in the outputinterfaces of the Address Generator (addrgen/predread/psgsync,addrgen/ip_wrt2/sync18 and addrgervp_rd2/sync18) and in the blocks whichcontrol the “swinging” of the swing-buffer RAMs in the DRAM Interface(see section on the DRAM Interface). In each case, the synchronizationprocess is achieved by means of three metastable-hard flip-flops inseries. It should be noted that this means that clk0/clk1 are used inthe output stages of the Address Generator.

[2752] In addition to these completely asynchronous clock regimes, thereare a number of separate clock generators which generate two-phasenon-overlapping clocks (ph0, ph1) from pllsysclk. The Address Generator,Prediction Filters and DRAM Interface each have their own clockgenerators; the remainder of the chip is run off a common clockgenerator. The reasons for this are twofold. First, it reduces thecapacitive load on individual clock generators, allowing smaller clockdrivers and reduced clock routing widths. Second, each scan path iscontrolled by a clock generator, so increasing the number of clockgenerators allows shorter scan-paths to be used.

[2753] It is necessary to resynchronize signals which are driven acrossthese clock-regime boundaries because the minor skews between thenon-overlapping clocks derived from different clock generators couldmean that underlap occurred at the interfaces. Circuitry built into each“Snooper” block (see Section B.11.4) ensures that this does not occur,and Snooper blocks have been placed at the boundaries between all theclock regimes, excepting at the front of the Address Generator, wherethe resynchronization is performed in the Token Decode block.

[2754] B.11.2 Control of Clocks

[2755] Each standard clock generator generates a number of differentclocks which allow operation in normal mode and scan-test mode. Thecontrol of clocks in scan-test mode is described in detail elsewhere,but it is worth noting that several of the clocks generated by a clockgenerator (tph0, tph1, tckm, tcks) do not usually appear to be joined toany primitive symbols on the schematics. This is because scan paths aregenerated automatically by a post-processor which correctly connectsthese clocks. From a functional point of view, the fact that thepost-processor has connected different clocks from those shown on theschematics can be ignored; the behavior is the same.

[2756] During normal operation, the master clocks can be derived inmanumber of differentways. Table B.11.1 indicates how various modes can beselected depending on the states of the pins pllselect and override.TABLE B.11.1 Clock Control Modes pllselect override Mode 0 0 pllsysclkis connected directly to external sysclk. bypassing the PLL; DRAMInterface clocks (cki0, cki1, ckq0, ckq1) are controlled directly fromthe pins ti and tq. 0 1 Override mode - ph0 and ph1 clocks arecontrolled directly from pins tphoish and tph1ish: DRAM Interface clocks(cki0, cki1, ckq0, ckq1) are controlled directly from the pins ti andtq. 1 0 Normal operation. pllsysclk is the clock generated by the PLL;DRAM Interface clocks are generated by PLL. 1 1 External resistorsconnected to ti and tq are used instead of the internal resistors (debugonly).

[2757] B.11.3 The Two-vire Interface

[2758] The overall functionality of the two-wire interface is describedin detail in the Technical Reference. However, the two-wire interface isused for all block-to-block communication within the Temporal Decoderand most blocks consist of a number of pipeline stages, all of which arethemselves two-wire interface stages. It is, therefore, essential tounderstand the internal implementation of the two-wire interface inorder to be able to interpret many of the schematics. In general, theseinternal pipeline stages are structured as shown in FIG. 143.

[2759]FIG. 143 shows a latch-logic-latch representation as this is theconfiguration which is normally used. However, when a number of stagesare put together, it is equally valid to think of a “stage” as beinglatch-latch-logic (for many engineers a more familiar model). The use ofthe latch-logic-latch configuration allows all inter-block communicationto be latch to latch, without any intervening logic in either thesending or receiving block.

[2760] Referring again to FIG. 143, a simple two-wire interface FIFOstage can be constructed by removing the logic block, connecting thedata and valid signals directly between the latches and the latchedin_valid directly into the NOR gate on the input to the in_accept latchin the same way as out_valid and out_accept are gated. Data and validsignals then propagate when the corresponding accept signal is high. ByORing in_valid with out_accept_reg in the manner shown, data will beaccepted if in_valid in low, even if out_accept_reg is low. In this waygaps (data with the valid bit low) are removed from the pipelinewhenever a stall (accept signal low) occurs.

[2761] With the logic block inserted, as shown in FIG. 143, in_acceptand out_valid may also be dependent on the data or the state of theblock. In the configuration shown, it is standard for any state withinthe block to be held in master-slave devices with the master enabled byph1 and the slave enabled by ph0.

[2762] B.11.4 Snooper Blocks

[2763] Snooper blocks enable access to the data stream at various pointsin the chip via the Microprocessor Interface. There are two types ofsnooper blocks. Ordinary Snoopers can only be accessed in test modewhere the clocks can be controlled directly. “Super Snoopers” can beaccessed while the clocks are running and contain circuitry whichsynchronizes the asynchronous data from the Microprocessor bus to theinternal chip clocks. Table B.11.2 lists the locations and types of allSnoopers in the Temporal Decoder. TABLE B.11.2 Snoopers in TemporalDecoder Location Type addrgervvec_pipe/snoopz31 Snooperaddrgervent_pipe/midsnp Snooper addrtgervent_pipe/endsnp Snooperaddrgervprecread/snoopz44 Snooper addrgervip_wrt2/superz10 Super Snooperaddrgervip_rd2/superz10 Super Snooper dramx/dramit/ifsnoops/snoopz15(fsnp) Snooper dramx/dramit/ifsnoops/snoopz15 (bsnp) Snooperdramx/dramit/ifsnoops/superz9 Super Snooper wrudder/superz9 SuperSnooper pfits/twdfit/dimbuff/snoopk13 Snooperpfits/bwdfit.dimbuff/snoopk13 Snooper pfits/snoopz9 Snooper

[2764] Details on the use of both Snoopers are contained in the testsection. Details of the operation of the JTAG interface are contained inthe JTAG documnent.

[2765] SECTION B.12 Functional Blocks

[2766] B.12.1 Top Fork

[2767] The Top Fork, in accordance with the present invention, servestwo different functions. First, it forks the data stream into twoseparate streams: one to the Address Generator and the other to theFIFO. Second, it provides the means of starting and stopping the chip sothat the chip can be configured.

[2768] The fork part aspect of the component is very simple. The samedata is presented to both the Address Generator and the FIFO, and has tohave been accepted by both blocks before an accept is sent back to theprevious stage. Thus, the valids of the two branches of the fork aredependent on the accepts from the other branch. If the chip is in astopped state, the valids to both branches are held low.

[2769] The chip powers up in a state where in accept is held low untilthe configure bit is set high. This ensures that no data is accepteduntil the user has configured the chip. If the user needs to configurethe chip at any other time, he must set the configure bit and wait untilthe chip has finished the current stream. The stopping process is asfollows:

[2770] 1)If the configure bit has been set, do not accept any more dataafter a flush token has been detected by the Top Fork.

[2771] 2)The chip will have finished processing the stream when theFLUSH Token reaches the Read Rudder. This causes the signal seq_done togo high.

[2772] 3)When seq_done goes high, set an event bit which can be read bythe Microprocessor. The event signal can be masked by the Event block.

[2773] B.12.2 Address Generator

[2774] In the present invention, the address generator (addrgen) isresponsible for counting the numbers of blocks within a frame, and forgenerating the correct sequence of addresses for DRAM data transfers.The address generator's input is the token stream from the token inputport (via topfork), and its output to the DRAM interface consists ofaddresses and other information, controlled by a request/acknowledgeprotocol.

[2775] The principal sections of the address generator are:

[2776] token decode

[2777] block counting and generation of the DRAM block address

[2778] conversion of motion vector data into an address offset

[2779] request and address generator for prediction transfers

[2780] reorder read address generator

[2781] write address generator

[2782] B.12.2.1 Token Decode (tokdec)

[2783] In the Token Decoder, tokens associated with coding standards,frame and block information and motion vectors are decoded. Theinformation extracted from the stream is stored in a set of registerswhich may also be accessed via the upi. The detection of a DATA tokenheader is signalled to subsequent blocks to enable block counting andaddress generation. Nothing happens when running JPEG.

[2784] List of tokens decoded:

[2785] CODING STANDARD

[2786] DATA

[2787] DEFINE_MAX_SAMPLING

[2788] DEFINEM_SAMPLING

[2789] HORIZONTAL_MBS

[2790] MVD_BACKWARDS

[2791] MVD_FORWARDS

[2792] PICTURE_START

[2793] PICTURE_TYPE

[2794] PREDICTION_MODE

[2795] This block also combines information from the request generatorsto control the toggling of the frame pointers and to stall the inputstream. The stream is stalled when a new frame appears at the input (inthe form of a PICTURE_START token) but the writeback or reorder readassociated with the previous frame is incomplete.

[2796] B.12.2.2 Macroblock Counter (mblkcntr)

[2797] The macroblock counter of the present invention consists of fourbasic counters which point to the horizontal and vertical position ofthe macroblock in the frame and to the horizontal and vertical positionof the block within the macroblock. At the beginning of time, and oneach PICTURE_START, all counters are reset to zero. As DATA Tokenheaders arrive, the counters increment and reset according to the colorcomponent number in the token header and the frame structure. This framestructure is described by the sampling registers in the token decoder.

[2798] For a given color component, the counting proceeds as follows.The horizontal block count is incremented on each new DATA Token of thesame component until it reaches the width of the macroblock, and then itresets. The vertical block count is incremented by this reset until itreaches the height of the macroblock, and then it resets. When thishappens, the next color component is expected. Hence, this sequence isrepeated for each of the components in the macroblock—the horizontal andvertical size of the macroblock, possibly being different for eachcomponent. If, for any component, fewer blocks are received than areexpected, the count will still proceed to the next component withouterror.

[2799] When the color component of the DATA Token is less than theexpected value, the horizontal macroblock count is incremented. (Notethat this will also occur when more than the expected number of blocksappear for a given color component, as the counters will then beexpecting a higher component index.) This horizontal count is reset whenthe count reaches the picture width in macroblocks. This resetincrements the vertical macroblock count.

[2800] There is a further ability to count macroblocks in H.261 CIFformat. In this case, there is an extra level hierarchy betweenmacroblocks and the picture called the group of blocks. This is elevenmacroblocks wide and three deep, and a picture is always two groupswide. The token decoder extracts the CIF bit from the PICTURE_TYPE tokenand passes this to the macroblock counter to instruct it to count groupsof blocks. Instances of too few or too many blocks per component willprovoke similar reactions as above.

[2801] B.12.2.3 Block Calculation (blkcalc)

[2802] The Block calculation converts the macroblock andblock-within-macroblock coordinates into coordinates for the block'sposition in the picture, i.e., it knocks out the level of hierarchy.This, of course, has to take into account the sampling ratios of thedifferent color components.

[2803] B.12.2.4 Base Block Address (bsblkadr)

[2804] The information from the blkcalc, together with the colorcomponent offsets, is used to calculate the block address within thelinear DRAM address space. Essentially, for a given color component, thelinear block address is the number of blocks down times the width of thepicture plus the number of blocks long. This is added to the colorcomponent offset to form the base block address.

[2805] B.12.2.5 Vector Offset (vec_pipe)

[2806] The motion vector information presented by the token decoder isin the form of horizontal and vertical pixel offset coordinates. Thatis, for each of the forward and backward vectors there is an (x,y) whichgives the displacement in half-pixels from the block being formed to theblock from which it is being predicted. Note that these coordinates maybe positive or negative. They are first scaled according to the samplingof each color component, and used to form the block and new pixel offsetcoordinates.

[2807] In FIG. 145, the shaded area represents the block that is beingformed. The dotted outline is the block from which it is beingpredicted. The big arrow shows the block offset—the horizontal andvertical vector to the DRAM block that contains the prediction block'sorigin—in this case (1,4). The small arrow shows the new pixeloffset—the position of the prediction block origin within that DRAMblock. As the DRAM block is 8×8 bytes, the pixel offset looks to be(7,2).

[2808] The multiplier array vmarrla then converts the block vectoroffset into a linear vector offset. The pixel information is passed tothe prediction request generator as an (x,y) coordinate (pix_info).

[2809] B.12.2.6 Prediction Requests

[2810] The frame pointer, base block address and vector offset are addedto form the address of the block to be fetched from the DRAM (Inblkad3).If the pixel offset is zero, only one request is generated. If there isan offset in either the x OR y dimension, then two requests aregenerated—the original block address and the one either immediately tothe right or immediately below. With an offset in both x and y, fourrequests are generated.

[2811] Synchronization between the chip clock regime and the DRAMinterface clock regime takes place between the first addition (Inblkad3)and the state machine that generates the appropriate requests. Thus, thestate machine (psgstate) is clocked by the DRAM interface clocks, andits scanned elements form part of the DRAM interface scan chain.

[2812] B.12.2.7 Reorder Read Requests and Write Requests

[2813] As there is no pixel offset involved here, each address is formedby adding the base block address to the relevant frame pointer. Thereorder read uses the same frame store as the prediction and data iswritten back to the other frame store. Each block includes a short FIFOto store addresses as the transfer of read and write data is likely tolag the prediction transfer at the corresponding address. (This isbecause the read/write data interacts with stream further along the chipdataflow than the prediction data). Each block also includessynchronization between the chip clock and the DRAM interface clock.

[2814] B.12.2.8 Offsets

[2815] The DRAM is configured as two frame stores, each of whichcontains up to three color components. The frame store pointers and thecolor component offsets within each frame must be programmed via theupi.

[2816] B.12.2.9 Snoopers

[2817] In the present invention, snoopers are positioned as follows:

[2818] Between blkcalc and bsblkadr—this interface comprises thehorizontal and vertical block coordinates, the appropriate colorcomponent offset and the width of the picture in blocks (for thatcomponent).

[2819] After bsblkadr—the base block address.

[2820] After vecpipe—the linear block offset, the pixel offset withinthe block, together with information on the prediction mode, colorcomponent and H.261 operation.

[2821] After Inblkad3—the physical block address, as described under“Prediction Requests”.

[2822] Super snoopers are located in the reorder read and write requestgenerators for use during testing of the external DRAM. See the DRAMInterface section for all the details.

[2823] B.12.2.10 Scan

[2824] The addrgen block has its own scan chain, the clocking of whichis controlled by the block's own clock generator (adclkgon). Note thatthe request generators at the back end of the block fall within the DRAMinterface clock regime.

[2825] B.12.3**Prediction Filters

[2826] The overall structure of the Prediction Filters, in accordancewith the present invention, is shown in FIG. 146. The forward andbackward filters are identical and filter the MPEG forward and backwardprediction blocks. Only the forward filter is used in H.261 mode (theh261_on input of the backward filter should be permanently low becauseH.261 streams do not contain backward predictions). The entirePrediction Filters block is composed of pipelines of two-wire interfacestages.

[2827] B.12.3.1 A Prediction Filter

[2828] Each Prediction Filter acts completely independently of theother, processing data as soon as valid data appears at its input. Itcan be seen from FIG. 147 that a Prediction Filter consists of fourseparate blocks, two of which are identical. It is best if the operationof these blocks is described independently for MPEG and H.261 operation.H.261 being the more complex, is described first.

[2829] B.12.3.1.1 H.261 Operation

[2830] The one-dimensional filter equation used is as follows:$\begin{matrix}{F_{i} = {\frac{x_{i + 1} + {2x_{i}} + x_{i - 1}}{4}( {1 \leq i \leq 6} )}} \\{F_{i} = {x_{i}({otherwise})}}\end{matrix}$

[2831] This is applied to each row of the 8×8 block by the x PredictionFilter and to each column by the y Prediction Filter. The mechanism bywhich this is achieved is illustrated in FIG. 148, which is basically arepresentation of the pfltldd schematic. The filter consists of threetwo-wire interface pipeline stages. For the first and last pixels in arow, registers A and C are reset and the data passes unaltered throughregisters B, D and F (the contents of B and D being added to zero). Thecontrol of Bx2mux is set so that the output of register B is shiftedleft by one. This shifting is in addition to the one place which it isalways shifted in any event. Thus, all values are multiplied by 4 (moreof this later). For all other pixels, x_(i+1) is loaded into register C,x_(i) into register B and x_(i−1) into register A. It can be seen fromFIG. 148 that the H.261 filter equation is then implemented. Becausevertical filtering is performed in horizontal groups of three (see noteson the Dimension Buffer, below) there is no need to treat the first andlast pixels in a row differently. The control and the counting of thepixels within a row is performed by the control logic associated witheach 1-D filter. It should be noted that the result has not been dividedby 4. Division by 16 (shift right by 4) is performed at the input of thePrediction Filters Adder (Section B.12.4.2) after both horizontal andvertical filtering has been performed, so that arithmetic accuracy isnot lost:. Registers DA, DD and DF pass control information down thepipeline. This includes h261_on and last_byte.

[2832] Of the other blocks found in the Prediction Filter, the functionof the Formatter is merely to ensure that data is presented to thex-filter in the correct order. It can be seen above that this merelyrequires a three-stage shift register, the first stage being connectedto the input of register C, the second to register B and the third toregister A.

[2833] Between the x and y filters, the Dimension Buffer buffers data sothat groups of three vertical pixels are presented to the y-filter.These groups of three are still processed horizontally, however, so thatno transposition occurs within the Prediction Filters. Referring to FIG.149, the sequence in which pixels are output from the Dimension Bufferis illustrated in Table B.12.1. TABLE B.12.1 H.261 Dimension BufferSequence Clock Input Pixel Output Pixel Clock Input Pixel Output Pixel 10  55(a) 17 16 7 2 1 56 18 17 F(0.8.15)(t) 3 2 57 19 18 F(1.9.17) 4 3 5820 19 F(2.10.16) 5 4 59 21 20 F(3.11.19) 6 5 60 22 21 F(4.12.30) 7 6 6123 22 F(5.13.31) 8 7 62 24 23 F(5.14.22) 9 8 63 25 24 F(7.15.23) 10 9  025 25 F(8.16.24) 11 10  1 27 26 F(9.17.25) 12 11  2 28 27 F(10.18.26) 1312  3 29 28 F(11.19.27) 14 13  4 30 29 F(12.20.28) 15 14  5 31 30F(12.20.28) 16 15  6 32 31 F(14.22.30)

[2834] B.12.3.1.2 MPEG Operation

[2835] During MPEG operation, a Prediction Filter performs a simple halfpel interpolation: $\begin{matrix}{F_{i} = {\frac{x_{i} + x_{i + 1}}{2}( {{0 \leq i \leq 8},{{half}\quad {pel}}} )}} \\{F_{i} = {x_{i}( {{0 \leq i \leq 7},{{integer}\quad {pel}}} )}}\end{matrix}$

[2836] This is the default filter operation unless the h261_on input islow. If the signal dim into a 1-D filter is low then integer pelinterpolation will be performed. Accordingly, if h261_on is low and xdimand ydim are low, all pixels are passed straight through withoutfiltering. It is an obvious requirement that when the dim signal into a1-D filter is high, the rows (or columns) will be 8 pixels wide (orhigh). This is summarized in Table B.12.2. Referring to FIG. 148, “1-DPrediction Filter,”, the TABLE B.12.2 1-D Filter Operation h261_on xdimydim Function 0 0 0 F₁ = x₁ 0 0 1 MPEG 8x9 block 0 1 0 MPEG 9x8 block 01 1 MPEG 9x9 block 1 0 0 H.261 Low-pass Filter 1 0 1 Illegal 1 1 0Illegal 1 1 1 Illegal

[2837] operation of the 1-D filter is the same for MPEG inter pel as itis for the first and last pixels in a row in H.261. For MPEG half-peloperation, register A is permanently reset and the output of register Cis shifted left by 1 (the output of register B is always shifted left by1 anyway). Thus, after a couple of clocks register F contains (2B +2C),four times the required result, but this is taken care of at the inputof the Prediction Filters Adder, where the number, having passed throughboth x and y filters, is shifted right by 4.

[2838] The function of the Formatter and Dimension Buffer are alsosimpler in MPEG. The formatter must collect two valid pixels beforepassing them to the x-filter for half-pel interpolation; the DimensionBuffer only needs to buffer one row. It is worth noting that after datahas passed through the x-filter, there can only ever be 8 pixels in arow, because the filtering operation converts 9-pixel rows into 8-pixelrows. “Lost” pixels are replaced by gaps in the data stream. Whenperforming half-pel interpolation, the x-filter inserts a gap at the endof each row (after every 8 pixels); the y-filter inserts 8 gaps at theend of the block. This is significant because the group of 8 or 9 gapsat the end of a block align with DATA Token headers and other tokensbetween DATA Tokens in the stream coming out of the FIFO. This minimizesthe worst-case throughput of the chip which occurs when 9×9 blocks arebeing filtered.

[2839] B.12.3.2 The Prediction Filters Adder.

[2840] During MPEG operation, predictions may be formed using an earlierpicture, a later picture, or the average of the two. Predictions formedfrom an earlier frame termed forward predictions and those formed from alater frame are called backward predictions. The function of thePrediction Filters Adder (pfadd) is to determine which filteredprediction values are being used (forward, backward or both) and eitherpass through the forward or backward filtered predictions or the averageof the two (rounded towards positive infinity).

[2841] The prediction mode can only change between blocks, i.e., atpower-up or after the fwd_(—)1st_byte and/or bwd_(—)1st_byte signals areactive, indicating the last byte of the current prediction block. If thecurrent block is a forward prediction then only fwd_(—)1st_byte isexamined. If it is a backward prediction then only bwd_(—)1st_byte isexamined. If it is a bidirectional prediction, then both fwdlstbyte andbwd_(—)1st_byte are examined.

[2842] The signals fwd_on and bwd_on determine which prediction valuesare used. At any time, either both or neither of these signals may beactive. At start-up, or if there is a gap when no valid data is presentat the inputs of the block, the block enters a state when neither signalis active.

[2843] Two criteria are used to determine the prediction mode for thenext block: the signals fwd_ima_twin and bwd_ima_twin, which indicatewhether a forward or backward block is part of a bidirectionalprediction pair, and the buses fwd_p_num[1:0] and bwd_p_num]1:0]. Thesebuses contain numbers which increment by one for each new predictionblock or pair of prediction blocks. These blocks are necessary because,for example, if there are two forward prediction blocks followed by abidirectional prediction block, the DRAM interface can fetch thebackward block of the bidirectional prediction sufficiently far ahead sothat it reaches the input of the Prediction Filters Adder before thesecond of the forward prediction blocks. Similarly, other sequences ofbackward and forward predictions can get out of sequence at the input ofthe Prediction Filters Adder. Thus, the next prediction mode isdetermined as follows:

[2844] 1)If valid forward data is present and fwd_ima_twin is high, thenthe block stalls until valid backward data arrives with bwd_ima_twin setand then it goes through the blocks averaging each pair of predictionvalues.

[2845] 2)If valid backward data is present and bwd_ima_twin is high,then the block stalls until valid forward data arrives with fwd_ima_twinset and then it proceeds as above. If forward and backward data arevalid together, there is no stall.

[2846] 3)If valid forward data is present, but fwd_ima_twin is not set,then fwd_p_num is examined. If this equals the number from the previousprediction plus one (stored in prednum) then the prediction mode is setto forward.

[2847] 4)If valid backward data is present but bwd_ima_twin is not set,then bwd_p_num is examined. If this equals the number from the previousprediction plus one (stored in prednum) then the prediction mode is setto backward.

[2848] Note that “early_valid” signals from one stage back in thepipeline are used so that the Prediction Filters Adder mode can be setup before the first data from a new block arrives. This ensures that nostalls are introduced into the pipeline.

[2849] The ima_twin and pred_num signals are not passed along theforward and backward prediction filter pipelines with the filtered data.This is because:

[2850] 1)These signals are only examined when fwd_(—)1st_byte and/orbwd_(—)1st_byte are valid.

[2851] This saves about 25 three-bit pipeline stages in each predictionfilter.

[2852] 2)The signals remain valid throughout a block and, therefore, arevalid at the time when fwd_(—)1st_byte and/or bwd_(—)1st_byte reach thePrediction Filters Adder.

[2853] 3)The signals are examined a clock before data arrives anyway.

[2854] B.12.4 Prediction Adder and FIFO

[2855] The prediction adder (padder) forms the predicted frame by addingthe data from the prediction filters to the error data. To compensatefor the delay from the input through the address generator, DRAMinterface and prediction filters, the error data passes through a 256word FIFO (sfifo) before reaching padder.

[2856] The CODING_STANDARD, PREDICTION_MODE and DATA Tokens are decodedto determine when a predicted block is being formed. The 8-bitprediction data is added to the 9-bit two's complement error data in theDATA Token. The result is restricted to the range 0 to 255 and passes tothe next block. Note that this data restriction also applies to allintra-coded data, including JPEG.

[2857] The prediction adder of the present invention also includes amechanism to detect mismatches in the data arriving from the FIFO andthe prediction filters. In theory, the amount of data from the filtersshould exactly correspond to the number of DATA Tokens from the FIFOwhich involve prediction. In the event of a serious malfunction,however, padder will attempt to recover.

[2858] The end of the data blocks from the FIFO and filters are marked,respectively, by the in_extn and fl_last inputs. Where the end of thefilter data is detected before the end of the DATA Token, the remainderof the token continues to the output unchanged. If, on the other hand,the filter block is longer than the DATA Token, the input is stalleduntil all the extra filter data has been accepted and discarded.

[2859] There is no snooper in either the FIFO or the prediction adder,as the chip can-be configured to pass data from the token input portdirectly to these blocks, and to pass their output directly to the tokenoutput port.

[2860] B.12.5 Write and Read Rudders

[2861] B.12.5.1 The Write Rudder (Wrudder)

[2862] The Write Rudder passes all tokens coming from the PredictionAdder on to the Read Rudder. It also passes all data blocks in I or Ppictures in MPEG, and all data blocks in H.261 to the DRAM interface sothat they can be written back into the external frame stores under thecontrol of the Address Generator. All the primary functionality iscontained within one two-wire interface stage, although the write-backdata passes through a snooper on its way to the DRAM interface.

[2863] The Write-Rudder decodes the following tokens: B.12.3 TokensDecoded by the Write Rudder Token Name Function in Write RudderCODING_STANDARD Write-back is inhibited for JPEG streams. PICTURE_TYPEWrite-back only occurs in I and P frames, not B frames. DATA Only thedata within DATA tokens is written back.

[2864] After the DATA Token header has been detected, all data bytes areoutput to the DRAM Interf ace. The end of the DATA Token is detected byin extn going low and this causes a flush signal to be sent to the DRAMInterface swing buffer. In normal operation, this will align with thepoint when the swing buffer would swing anyway, but if the DATA Tokendoes not contain 64 bytes of data this provides a recovery mechanism(although it is likely that the next few output pictures would beincorrect).

[2865] B.12.5.2 The Read Rudder (rrudder)

[2866] The Read Rudder of the present invention has three functions, thetwo major ones relating to picture sequence reordering in MPEG:

[2867] 1)To insert data which has been read-back from the external framestore into the token stream at the correct places.

[2868] 2)To reorder picture header information in I and P pictures.

[2869] 3)To detect the end of a token stream by detecting the FLUSHtoken (see Section B.12.1, “Top Fork”).

[2870] The structure of the Read Rudder is illustrated in FIG. 150. Theentire block is made from standard two-wire interface technology. Tokensin the input interface latches are decoded and these decodes determinethe operation of the block: TABLE B.12.4 Tokens decoded by the ReadRudder Token Name Function in Read Rudder FLUSH Signals to Top Fork.CODING_STANDARD Reordering is inhibited if the coding standard is notMPEG. SEQUENCE_START The read-back data for the first picture of areordered sequence is invalid PICTURE_START Signals that the currentoutput FIFO must be swapped (I or P pictures). The first of the pictureheader tokens. PICTURE_END All tokens above the picture layer areallowed through TEMPORTAL_REFERENCE The second of the picture headertokens. PICTURE_TYPE The third of the picture header tokens. DATA Whenreordering, the contents of DATA tokens are replaced with reordereddata.

[2871] The reorder function is turned on via the MicroprocessorInterface, but is inhibited if the coding standard is not MPEG,regardless of the state of the register. The same MPI register controlswhether the Address Generator generates a reorder address and thus,reorder is an output from this block. To understand how the Read Rudderworks, consider the input and output control logic separately, bearingin mind that the sequence of tokens is as follows:

[2872] CODING_STANDARD

[2873] SEQUENCE_START

[2874] PICTURE_START

[2875] TEMPORAL_REFERENCE

[2876] PICTURE_TYPE

[2877] Picture containing DATA Tokens and other tokens

[2878] PICTURE_END

[2879] . . .

[2880] PICTURE_START

[2881] . . .

[2882] B.12.5.2.1 Input Control Locic

[2883] From the power-up, all tokens pass into FIFO 1 (called thecurrent input FIFO) until the first PICTURE_TYPE token for an I or Ppicture is encountered. FIFO 2 then becomes the current input FIFO andall input is directed to it until the next PICTURE_TYPE for an I or Ppicture is encountered and FIFO 1 becomes the current input FIFO again.Within I and P pictures, all tokens between PICTURE_TYPE andPICTURE_END, except DATA Tokens, are discarded. This is to preventmotion vectors, etc. from being associated with the wrong pictures inthe reordered stream, where they would have no meaning.

[2884] A three-bit code is put into the FIFO, along with the tokenstream, to indicate the presence of certain token headers. This saveshaving to perform token decoding on the output of the FIFOs.

[2885] B.12.5.2.2 output Control Logic

[2886] From the power-up, tokens are accepted from FIFO 1 (called thecurrent output FIFO) until a picture start code is encountered, afterwhich FIFO 2 becomes the current output FIFO. Referring back to SectionB.12.5.2.1, it can be seen that at this stage the three picture headertokens, PICTURE_START, TEMPORAL_REFERENCE and PICTURE_START are retainedin FIFO 1. The current output FIFO is swapped every time a picture startcode isencountered in an I or P frame. Accordingly, the three pictureheader tokens are stored until the next I or P frame, at which time theywill become associated with the correctly reordered data. B pictures arenot reordered and, hence, pass through without any tokens beingdiscarded. All tokens in the first picture, including PICTURE_END arediscarded.

[2887] During I and P pictures, the data contained in DATA Tokens in thetoken stream is replaced by reordered data from the DRAM Interface.During the first picture, “reordered” data is still present at thereordered data input because the Address Generator still requests theDRAM Interface to fetch it. This is considered garbage and is discarded.

[2888] SECTION B.13 The DRAM Interface

[2889] B.13.1 Overview

[2890] In the present invention, the Spatial Decoder, Temporal Decoderand Video Formatter each contain a DRAM Interface block for thatparticular chip. In all three devices, the function of the DRAMInterface is to transfer data from the chip to the external DRAM andfrom the external DRAM into the chip via block addresses supplied by anaddress generator.

[2891] The DRAM Interface typically operates from a clock which isasynchronous to both the address generator and to the clocks of thevarious blocks through which data is passed. This asynchronism isreadily managed, however, because the clocks are operating atapproximately the same frequency. Data is usually transferred betweenthe DRAM Interface and the rest of the chip in blocks of 64 bytes (theonly exception being prediction data in the Temporal Decoder) Transferstake place by means of a device known as a “swing buffer”. This isessentially a pair of RAMs operated in a double-buffered configuration,with the DRAM interface filling or emptying one RAM while another partof the chip empties or fills the other RAM. A separate bus which carriesan address from an address generator is associated with each swingbuffer.

[2892] Each of the chips has four swing buffers, but the function ofthese swing buffers is different in each case. In the Spatial Decoder,one swing buffer is used to transfer coded data to the DRAM, another toread coded data from the DRAM, the third to transfer tokenized data tothe DRAM and the fourth to read tokenized data from the DRAM. In theTemporal Decoder, one swing buffer is used to write Intra or Predictedpicture data to the DRAM, the second to read Intra or Predicted datafrom the DRAM and the other two to read Intra or Predicted data from theDRAM and the other two to read forward and backward prediction data. Inthe Video Formatter, one swing buffer is used to transfer data to theDRAM and the other three are used to read data from the DRAM, one ofeach of Luminance (Y) and the Red and Blue color difference data (Cr andCb respectively).

[2893] The operation of the generic features of the DRAM Interface isdescribed in the Spatial Decoder document. The following sectiondescribes the features peculiar to the Temporal Decoder.

[2894] B.13.2 The Temporal Decoder DRAM Interface

[2895] As mentioned in section B.13.1, the Temporal Decoder has fourswing buffers: two are used to read and write decoded Intra andPredicted (I and P) picture data and these operate as described above.The other two are used to fetch prediction data.

[2896] In general, prediction data will be offset from the position ofthe block being processed as specified by motion vectors in x and y.Thus, the block of data to be fetched will not generally correspond tothe block boundaries of the data as it was encoded (and written into theDRAM). This is illustrated in FIGS. 151 and 25, where the shaded arearepresents the block that is being formed. The dotted outline shows theblock from which it is being predicted. The address generator convertsthe address specified by the motion vectors to a block offset (a wholenumber of blocks), as shown by the big arrow, and a pixel offset, asshown by the little arrow.

[2897] In the address generator, the frame pointer, base block addressand vector offset are added to form the address of the block to befetched from the DRAM. If the pixel offset is zero, only one request isgenerated. If there is an offset in either the x or y dimension, thentwo requests are generated the original block address and the one eitherimmediately to the right or immediately below. With an offset in both xand y, four requests are generated. For each block which is to befetched, the address generator calculates start and stop addressesparameters and passes these to the DRAM interface. The use of thesestart and stop addresses is best illustrated by an example, as outlinedbelow.

[2898] Consider a pixel offset of (1, 1), as illustrated by the shadedarea in FIG. 152 and FIG. 26. The address generator makes four requests,labelled A through D in the figure. The problem to be solved is how toprovide the required sequence of row addresses quickly. The solution isto use “start/stop” technology, and this is described below.

[2899] Consider block A in FIG. 152. Reading must start at position(1, 1) and end at position (7, 7). Assume for the moment that one byteis being read at a time (i.e. an 8 bit DRAM Interface). The x value inthe coordinate pair forms the three LSBs of the address, the y value thethree MSBs. The x and y start values are both 1, giving the address 9.Data is read from this address and the x value is incremented. Theprocess is repeated until the x value reaches its stop value. At thispoint, the y value is incremented by 1 and the x start value isreloaded, giving an address of 17. As each byte of data is read, the xvalue is again incremented until it reaches its stop value. The processis repeated until both x and y values have reached their stop values.Thus, the address sequence of 9, 10, 11, 12, 13, 14, 15, 17, . . ., 23,25, . . ., 31, 33, . . . , . . . , 57, . . ., 63 is generated.

[2900] In a similar manner, the start and stop coordinates for block Bare: (1, 0) and (7, 0), for block C: (0,1) and (0,7), and for block D:(0, 0) and (0, 0).

[2901] The next issue is where this data should be written. Clearly,looking at block A, the data read from address 9 should be written toaddress 0 in the swing buffer, the data from address 10 to address 15 inthe swing buffer, and so on. Similarly, the data read from address 8 inblock B should be written to address 15 in the swing buffer and the datafrom address 16 into address 15 in the swing buffer. This function turnsout to have a very simple implementation as outlined below.

[2902] Consider block A. At the start of reading, the swing bufferaddress register is loaded with the inverse of the stop value, the yinverse stop value forming the 3 MSBs and the x inverse stop valueforming the 3 LSBs. In this case, while the DRAM Interface is readingaddress 9 in the external DRAM, the swing buffer address is zero. Theswing buffer address register is then incremented as the external DRAMaddress register is incremented, as illustrated in Table B.13.1: TABLEB.13.1 Illustration of Prediction Addressing Ext Swing DRAM Ad. Buff Ad.Ext DRAM Address Swing Buff Address (Binary) (Binary)  9 = y-start,x-start 0 = {overscore (y-stop)}, {overscore (x-stop)} 001 001 000 00010 1 111 110 000 001 11 2 001 011 000 010 15 6 001 111 000 110 17 = y+1,x-start 8 = y+1, {overscore (x-stop)} 010 001 001 000 18 9 010 010 001001

[2903] The discussion thus far has centered an an 8 bit DRAM Interface.In the case of a 16 or 32 bit interface, a few minor modifications mustbe made. First, the pixel offset vector must be “clipped” so that itpoints to a 16 or 32 bit boundary. In the example we have been using,for block A, the first DRAM read will point to address 0, and data inaddresses 0 through 3 will be read. Next, the unwanted data must bediscarded. This is performed by writing all the data into the swingbuffer (which must now be physically bigger than was necessary in the 8bit case) and reading with an offset. When performing MPEG half-pelinterpolation, 9 bytes in x and/or y must be read from the DRAMInterface. In this case, the address generator provides the appropriatestart and stop addresses and some additional logic in the DRAM Interfaceis used, but there is no fundamental change in the way the DRAMInterface operates.

[2904] The final point to note about the Temporal Decoder DRAM Interfaceis that additional information must be provided to the predictionfilters to indicate what processing is required on the data. Thisconsists of the following:

[2905] a “last byte” signal indicating the last byte of a transfer (of64, 72 or 81 bytes)

[2906] an H.261 flag

[2907] a bidirectional prediction flag

[2908] two bits to indicate the block's dimensions (8 or 9 bytes in xand y)

[2909] a two bit number to indicate the order of the blocks

[2910] The last byte flag can be generated as the data is read out ofthe swing buffer. The other signals are derived from the addressgenerator and are piped through the DRAM Interface so that they areassociated with the correct block of data as it is read out of the swingbuffer by the prediction filter block.

[2911] SECTION B.14 UPI Documentation

[2912] B.14.1 Introduction

[2913] This document is intended to give the reader an appreciation ofthe operation of the microprocessor interface in accordance with thepresent invention. The interface is basically the same on both theSPATIAL DECODER and the Temporal Decoder, the only difference being thenumber of address lines.

[2914] The logic described here is purely the microprocessor internallogic. The relevant schematics are:

[2915] UPI

[2916] UPI101

[2917] UPI102

[2918] DINLOGIC

[2919] DINCELL

[2920] UPIN

[2921] TDET

[2922] NONOVRLP

[2923] WRTGEN

[2924] READGEN

[2925] VREFCKT

[2926] The circuits UPI, UPI101, UPI102 are all the same except that theUPI01 has a 7 bit address input with the 8th bit hardwired to ground,while the other two have an 8 bit address input.

[2927] Input/Output Signals

[2928] The signals described here are a list of all the inputs andoutputs (defined with respect to the UPI) to the UPI module with a notedetailing the source or destination of these signals:

[2929] NOTRSTInputGlobal chip reset, active low, from Pad Input Driver

[2930] E1InputEnable signal 1, active low, from the Pad Input Driver(Schmitt).

[2931] E2InputEnable signal 2, active low, from the Pad Input Driver(Schmitt).

[2932] RNOTWInputRead not write signal from the Pad Input Driver(Schmitt).

[2933] ADDRIN[7:0]InputAddress bus signals from the Pad Input Drivers(Schmitt).

[2934] NOTDIN[7:0]Inputlnput data bus from the Input Pad Drivers of theBi-directional Microprocessor Data pins (TTLin).

[2935] INT_RNOTWOutputThe Internal Read not Write signal to the internalcircuitry being accessed by microprocessor interface (See memory map).

[2936] INT_ADDR[7:0]OutputThe Internal Address Bus to all the circuitsbeing accessed by the microprocessor interface (See memory map).

[2937] INTDBUS[7:0]Input/OutputThe Internal Data bus to all the circuitsbeing accessed by the microprocessor interface (See the memory map) andalso the microprocessor data output pads. The internal Data bustransfers data which is the inverse to that on the pins of the chip.

[2938] READ_STRoutputAn is an internal timing signal which indicates aread of a location in the device memory map.

[2939] WRITE_STRoutputAn is an internal signal which indicates a writeof a location in the internal memory map.

[2940] TRISTATEDPADOutputAn is an internal signal which connects to themicroprocessor data output pads which indicates that they should betristate.

[2941] General Comments:

[2942] The UPI schematic consists of 6 smaller modules: NONOVRLP, UPIN,DINLOGIC, VREFCKT, READGEN, WRTGEN. it should be noted from the overalllist of signals that there are no clock signals associated with themicroprocessor interface other than the microprocessor bus timingsignals which are asynchronous.to all the other timing signals on thechip. Therefore, no timing relationship should be assumed between theoperation of the microprocessor and the rest of the device other thanthose that can be forced by external control. For example, stopping ofthe System clock externally while accessing the microprocessor interfaceon a test system.

[2943] The other implication of not having a clock in the UPI is thatsome internal timing is self timed. That is, the delay of some signalsis controlled internally to the UPI block.

[2944] The overall function of the UPI is to take the address, data andenable and read/write signals from the outside world and format them sothat they can drive the internal circuits correctly. The internalsignals that define access to the memory map are INT_RNOTWINT_ADDR[. . .], INTDBUS[. . .] and READ_STR and WRITE_STR. The timing relationship ofthese signals is shown below for a read cycle and a write cycle. Itshould be noted that although the datasheet definition and the followingdiagram always shows a chip enable cycle, the circuit operation is suchthat the enable can be held low and the address can be cycled to dosuccessive read or write operations. This function is possible becauseof the address transition circuits.

[2945] Also, the presence of the INT_RNOTW and the READ_STR, WRITE_STRdoes reflect some redundancy. It allows internal circuits to use eithera separate READ_STR and WRITE_STR (and ignore INT_RNOTW) or to use theINT_RNOTW and a separate Strobe signal (Strobe signal being derived fromOR of READ_STR and WRITE_STR).

[2946] The internal databus is precharged High during a read cycle andit also has resistive pullups so that for extended periods when theinternal data bus is not driven it will default to the 0×FF condition.As the internal databus is the inverse of the data on the pins, thistranslates to 0×00 on the external pins, when they are enabled. Thismeans that, if any external cycle accesses a register or a bit of aregister which is a hole in the memory map, then the output data iddeterminate and is Low.

[2947] Circuit Details:

[2948] UPIN

[2949] This circuit is the overall change detect block. It contains asub-circuit called TDET which is a single bit change detect circuit.UPIN has a TDET module for each address bit and rnotw and for eachenable signal. UPIN also contains some combinatorial logic to gatetogether the outputs of the change detect circuits. This gatinggenerates the signals:

[2950] TRAN—which indicates a transition on one of the input signals,and

[2951] UPD-DONE—which indicates that transitions have been completed anda cycle can be performed.

[2952] CHIPEN—which indicates that the chip has been selected.

[2953] TDET

[2954] This is the single bit change detect circuit. It consists of a 2latches, and 2 exclusive OR gates. The first latch is clocked by thesignal SAMPLE and the second by the signal UPDATE. These twonon-overlapping signals come from the module NONOVRLP. The generaloperation is such that an input transition causes a CHANGE which, inturn, causes a SAMPLE. All input changes while SAMPLE is high areaccepted and when input changes cease then CHANGE goes low and SAMPLEgoes low which causes UPDATE to go high which then transfers data to theoutput latch and indicates UPD_DONE.

[2955] NONOVRLP

[2956] This circuit is basically a non-overlapping clock generator whichinputs TRAN and generates SAMPLE and UPDATE. The external gating on theoutput of UPDATE stops UPDATE from going high until a write pulse hasbeen completed.

[2957] DINLOGIC

[2958] This module consists of eight instances of the data input circuitDINCELL and some gating to drive the TRISTATEPAD signal. This indicatesthat the output data port will only drive if Enable1 is low, Enable2 islow, RnotW is high and the internal read_str is high.

[2959] DINCELL

[2960] This circuit consists of the data input latch and a tristatedriverto drive the internal databus. Data from the input pad is latchedwhen the signal DATAHOLD is high and when both Enable1 and Enable2 arelow. The tristate driver drives the internal data bus whenever theinternal signal INTRNOTW is low. The internal databus prechargetransistor and the bus pullup are also included in this module.

[2961] WRTGEN

[2962] This module generates the WRITE_STR, and the latch signalDATAHOLD for the data latches. The write strobe is a self timed signal,however, the self time delay is defined in the VREFCKT. The output fromthe timing circuit RESETWRITE is used to terminate the WRITE_STR signal.It should be noted that the actual write pulse which writes a registeronly occurs after an access cycle is concluded. This is because the datainput to the chip is sampled only on the back edge of the cycle. Hence,data is only valid after a normal access cycle has concluded.

[2963] READGEN

[2964] This circuit, as its name suggests, generates the READ_STR and italso generates the PRECH signal which is used to precharge the internaldatabus. The PRECH signal is also a self timed signal whose period isdependant on VREFCKT and also on the voltage on the internal databus.The READ_STR is not self timed, but lasts from the end of the prechargeperiod until the end of the cycle. The precharge circuitry usesinverters with their transfer characteristic biased so that they need avoltage of approximately 75% of supply before they invert. This circuitguarantees that the internal bus is correctly precharged before aREAD_STR begins. In order to stop a PRECH pulse tending to zero width ifthe internal bus is already precharged, the timing circuit guarantees aminimum, width via the signal RESETREAD.

[2965] VRFCKT

[2966] The VREFCKT is the only circuit which controls the self timing ofthe interface. Both the delays, 1/Width of WRITE_STR and 2/Width ofPRECH, are controlled by a current through a P transistor. The gate onthis P transistor is controlled by a signal VREF and this voltage is setby a diffusion resistor of 25K ohm.

[2967] SECTION C.1 Overview

[2968] C.1.1. Introduction

[2969] The structure of the image Formatter, in accordance with thepresent invention, is shown in FIG. 155. There are two addressgenerators, one for writing and one for reading, a buffer manager whichsupervises the two address generators and which provides frame-rateconversion, a data processing pipeline, including both vertical andhorizontal unsamplers, color-space conversion and gamma correction, anda final control block which regulates the output of the processingpipeline.

[2970] C.1.2 Buffer Manager

[2971] Tokens arriving at the input to the Image Formatter are bufferedin the FIFO and then transferred into the buffer manager. This blockdetects the arrival of new pictures and determines the availability of abuffer in which to store each picture. If there is a buffer available,it is allocated to the arriving picture and its index is transferred tothe write address generator If there is no buffer available, theincoming picture will be stalled until one becomes available. All tokensare passed on to the write address generator.

[2972] Each time the read address generator receives a VSYNC signal fromthe display system, a request is made to the buffer manager for a newdisplay buffer index. If there is a buffer containing complete picturedata, and that picture is deemed ready for display, then that buffer'sindex will be passed to the display address generator. If not, thebuffer manager sends the index of the last buffer to be displayed. Atstart-up, zero is passed as the index until the first buffer is full.

[2973] A picture is ready for display if its number (calculated as eachpicture is input) is greater than or equal to the picture number whichis expected at the display (presentation number) given the encodingframe rate. The expected number is determined by counting picture clockpulses, where picture clock can be generated either locally by the clockdividers, or externally. This technology allows frame-rate conversion(e.g., 2-3 pull-down).

[2974] External DRAM is used for the buffers, which can be either two orthree in number. Three are necessary if frame-rate conversion is to beeffected.

[2975] C.1.3 Write Address Generator

[2976] The write address generator receives tokens from the buffermanager and detects the arrival of each new DATA Token. As each DATAToken arrives, the address generator calculates a new address for theDRAM interface for storing the arriving block. The raw data is thenpassed to the DRAM interface where it is written into a swing buffer.Note that DRAM addresses are block addresses, and pictures in the DRAMor organized as rasters of blocks. Incoming picture data, however, isactually organized sequences of macroblocks, so the address generationalgorithm must take into account line-width (in blocks) offsets for thelower rows of blocks within the macroblock. The arrival buffer indexprovided by the buffer manager is used as an address offset for thewhole of the picture being stored. Furthermore, each component is storedin a separate area within the specified buffer, so component offsets arealso used in the calculation.

[2977] C.1.4 Read Address Generator

[2978] The Read Address Generator (dispaddr) does not receive orgenerate tokens, it generates addresses only. In response to a VSYNC, itmay, depending on field_info, read_start, sync_mode, and lsb_invert,request a buffer index from the buffer manager. Having received anindex, it generates three sets of addresses, one for each component, forthe current picture to be read in raster order. Different setups allowfor: interlaced/progressive display and/or data, vertical unsampling,and field synchronization (to an interlaced display). At the lowerlevel, the Read Address Generator converts base addresses into asequence of block addresses and byte counts for each of the threecomponents that are compatible with the page structure of the DRAM. Theaddresses provided to the DRA.M interface are page and line addressesalong with block start and block end counts.

[2979] C.1.5 Output Pipeline

[2980] Data from the DRAM interface feeds the output pipeline. The threecomponent streams are first vertically interpolated, then horizontallyinterpolated. Following the interpolators, the three components shouldbe of equal ratios (4:4:4), and are passed through the color-spaceconverter and color lookup tables/gamma correction. The output interfacemay hold the streams at this point until the display has reached anHSYSC. Thereafter, output controller directs the three components intoone, two or three 8-bit buses, multiplexing as necessary.

[2981] C.1.6 Timing Regimes

[2982] There are basically two principal timing regimes associated withthe Image Formatter. First, there is a system clock, which providestiming for the front end of the chip (address generators and buffermanager, plus the front end of the DRAM interface). Second, there is apixel clock which drives all the timing for the back end (DRAM interfaceoutput, and the whole of the output pipeline).

[2983] Each of the two aforementioned clocks drives a number of on-chipclock generators. The FIFO, buffer manager and read address generatoroperate from the same clock (DΦ) with the write address generator usinga similar, but separate clock (WΦ). Data is clocked into the DRAMinterface on an internal DRAM interface clock, (outΦ). DΦ WΦ and outΦare all generated from syscik.

[2984] Read and write addresses are clocked in the DRAM interface by theDRAM interface's own clock.

[2985] Data is read out of the DRAM interface on bifRΦ, and istransferred to the section of the output pipeline named “bushy_ne”(north-east—by virtue of its physical location) which operates on clocksdenoted by NEΦ. The section of the pipeline from the gamma RAMs onwardis clocked on a separate, but similar, clock (RΦ). bifRΦ, NEΦ and RΦ areall derived from the pixel clock, pixin.

[2986] For testing, all of the major interfaces between blocks haveeither snoopers or super-snoopers attached. This depends on the timingregimes and the type of access required. Block boundaries betweenseparate, but similar timing regimes have retiming latches associatedtherewith.

[2987] SECTION C.2 Buffer Management

[2988] C.2.1. Introduction

[2989] The purpose of the buffer management block, in accordance withthe present invention, is to supply the address generators with indicesidentifying any of either two or three external buffers for writing andreading of picture data. The allocation of these indices is influencedby three principal factors, each representing the effect of one of thetiming regimes in operation. These are the rate at which picture dataarrives at the input to Image Formatter (coded data rate), the rate atwhich data is displayed (display data rate), and the frame rate of theencoded video sequence (presentation rate).

[2990] C.2.2 Functional Overview

[2991] A three-buffer system allows the presentation rate and thedisplay rate to differ (e.g., 2-3 pulldown), so that frames are eitherrepeated or skipped as necessary to achieve the best possible sequenceof frames given the timing constraints of the system. Pictures whichpresent some difficulty in decoding may also be accommodated in asimilar way, so that if a picture takes longer than the availabledisplay time to decode, the previous frame will be repeated whileeverything else “catches up”. In a two-buffer system, the three timingregimes must be locked—it is the third buffer which provides theflexibility for taking up the slack.

[2992] The buffer manager operates by maintaining certain statusinformation associated with each external buffer. This includes flagsindicating if the buffer is in use, if it is full of data, or ready fordisplay, and the picture number within the sequence of the picturecurrently stored in the buffer. The presentation number is alsorecorded, this being a number which increments every time a pictureclock pulse is received, and represents the picture number which iscurrently expected for display based on the frame rate of the encodedsequence.

[2993] An arrival buffer (a buffer to which incoming data will bewritten) is allocated every time a PICTURE_START token is detected atthe input. This buffer is then flagged as IN_USE. On PICTURE_END, thearrival buffer will be de-allocated (reset to zero) and thebufferflagged as either FULL or READY depending on the relationship betweenthe picture number and the presentation number.

[2994] The display address generator requests a new display buffer, onceevery vsync, via a two-wire interface. If there is a buffer flagged asREADY, then that will be allocated to display by the buffer manager. Ifthere is no READY buffer, the previously displayed buffer will berepeated.

[2995] Each time the presentation number changes, it is detected andevery buffer containing a complete picture is tested for READY-ness byexamining the relationship between its picture number and thepresentation number. Buffers are considered in turn. When any of thebuffers are deemed to be READY, this automatically cancels theREADY-ness of any buffer which was previously flagged as READY. Theprevious buffer is then flagged as EMPTY. This works because laterpicture numbers are stored, by virtue of the allocation scheme, in thebuffers that are considered later.

[2996] TEMPORAL_REFERENCE tokens in H.261 cause a buffer's picturenumber to be modified if skipped pictures in the input stream areindicated. This feature, although envisioned, is not currently included,however. Similarly, TEMPORAL-REFERENCE tokens in MPEG have no effect.

[2997] A FLUSH token causes the input to stall until every buffer iseither EMPTY or has been allocated as the display buffer. Thereafter,presentation number and picture number are reset and a new sequence cancommence.

[2998] C.2.3 Architecture

[2999] C.2.3.1 Interfaces

[3000] C.2.3.1.1. Interface to bm Front

[3001] All data is input to the buffer manager from the input FIFO,bm_front. This transfer takes place via a two-wire interface, the databeing 8 bits wide plus an extension bit. All data arriving at the buffermanager is guaranteed to be a complete token. This is a necessity forthe continued processing of presentation numbers and display bufferrequests in the event of significant gaps in the data upstream.

[3002] C.2.3.1.2 Interface to Waddrcen

[3003] Tokens (8 bit data, 1 bit extension) are transferred to the writeaddress generator via a two-wire interface. The arrival buffer index isalso transferred on the same interface, so that the correct index isavailable for address generation at the same time as the PICTURE

START token arrives at waddrgen.

[3004] C.2.3.1.3 Interface to Dispaddr

[3005] The interface to the read address generator comprises twoseparate two-wire interfaces which can be considered to act as “request”and “acknowledge” signals, respectively. Single wires are not adequate,however, because of the two two-wire-based state machines at either end.

[3006] The sequence of events normally associated with the dispaddrinterface is as follows. First, dis-paddr invokes a request in responseto a vsync from the display device by asserting the drq_valid input tothe buffer manager. Next, when the buffer manager reaches an appropriatepoint in its state machine, it will accept the request and go aboutallocating a buffer to be displayed. Thereafter, the disp_valid wire isasserted, the buffer index is transferred, and this is typicallyaccepted immediately by dispaddr. Furthermore, there is an additionalwire associated with this last two-wire interface (rst_fld) whichindicates that the field number associated with the current index mustbe reset regardless of the previous field number.

[3007] C.2.3.1.4 Microprocessor Interface

[3008] The buffer manager block uses four bits of microprocessor addressspace, together with the 8-bit data bus and read and write strobes.There are two select signals, one indicating user-accessible locationsand the other indicating test locations which should not require accessunder normal operating conditions.

[3009] C.2.3.1.5 Events

[3010] The buffer manager is capable of producing two different events,index found and late arrival. The first of these is asserted when apicture arrives and its PICTURE_START extension byte (picture index)matches the value written into the BU_BM_TARGET_IX register at setup.The second event occurs when a display buffer is allocated and itspicture number is less than the current presentation number, i.e., theprocessing in the system pipeline up to the buffer manager has notmanaged to keep up with the presentation requirements.

[3011] C.2.3.1.6 Picture Clock

[3012] In the present invention, picture clock is the clock signal forthe presentation number counter and is either generated on-chip or takenfrom an external source (normally the display system). The buffermanager accepts both of these signals and selects one based on the valueof pclk_ext (a bit in the buffer manager's control register). Thissignal also acts as the enable for the pad picoutpad, so that if theImage Formatter is generating its own picture clock, this signal is alsoavailable as an output from the chip.

[3013] C.2.3.2. Major Blocks

[3014] The following sections describe the various hardware blocks thatmake up the buffer manager schematic (bmlogic).

[3015] C.2.3.2.1 Input/Output Block (bm Input)

[3016] This module contains all of the hardware associated with the fourtwo-wire interfaces of the buffer manager (input and output data,drq_valid/accept and disp_valid/accept). The input data register isshown, together with some token decoding hardware attached thereto. Thesignal vheader at the input to bm_tokdec is used to ensure that thetoken decoder outputs can only be asserted at a point where a headerwould be valid (i.e., not in the middle of a token. The rtimd block actsas the output data registers, adjacent to the duplicate input dataregisters for the next block in the pipeline. This accounts for timingdifferences due to different clock generators. Signals go and ngo arebased on the AND of data valid, accept and not stopped, and are usedelsewhere in the state machine to indicate if things are “bunged up” ateither the input or the output.

[3017] The display index part of this module comprises the two-wireinterfaces together with equivalent “go” signals as for data. Therst_fld bit also happens here, this being a signal which, if set,remains high until disp_valid has been high for one cycle. Thereafter,it is reset. In addition, rst_fld is reset after a FLUSH token hascaused all of the external buffers to be flagged either as EMPTY orIN_USE by the display buffer. This is the same point at which bothpicture numbers and presentation number are reset.

[3018] There is a small amount of additional circuitry associated withthe input data register which appears at the next level up thehierarchy. This circuitry produces a signal which indicates that theinput data register contains a value equal to that written intoBU_BM_TARG_IX and it is used for event generation.

[3019] C.2.3.2.2 Index Block (bm Index)

[3020] The Index block consists mainly of the 2-bit registers denotingthe various strategic buffer indices. These are arr_buf, the buffer towhich arriving picture data is being written, disp_buf, the buffer fromwhich picture data is being read for display, and rdy_buf, the index ofthe buffer containing the most up to date picture which could bedisplayed if a buffer was requested by dispaddr. There is also aregister containing buf_ix, which is used as a general pointer to abuffer. This register gets incremented (“D” input to mux) to cyclethrough the buffers examining their status, or which gets assigned thevalue of one of arr_buf, disp_buf or rdy_buf when the status needschanging. All of these registers (ph0 versions) are accessible from themicroprocessor as part of the test address space. Old_ix is just are-timed version of buf_ix and is used for enabling buffer status andpicture number registers in the bm stus block. Both buf_ix and old_ixare decoded into three signals (each can hold the value 1 to 3) whichare output from this block. Other outputs indicate whether buf_ix hasthe same value as either arr_buf or disp_buf, and whether either ofrdy_buf and disp_buf have the value zero. Zero is not a reference to abuffer. It merely indicates that there is no arrival/display/readybuffer currently allocated.

[3021] Arr_buf and disp_buf are enabled by their respective two-wireinterface output accept registers.

[3022] Additional circuitry at the bmlogic level is used to determine ifthe current buffer index (buf_ix) is equal to the maximum index in useas defined by the value written into the control register at setup. A“1” in the control register indicates a three-buffer system, and a “0”indicates a two-buffer system.

[3023] C.2.3.2.3 Buffer Status

[3024] The main components in the buffer status are status and picturenumber registers for each buffer. Each of the groups of three is amaster-slave arrangement where the slaves are the banks of threeregisters, and the master is a single register whose output is directedto one of the slaves (switched, using register enables, by old_ix). Oneof the possible inputs to the master is multiplexed between thedifferent slave outputs (indexed by buf_ix at the bmlogic level). Bufferstatus, which is decoded at the bmlogic level, for use in the statemachine logic can take any of the values shown in Table C.2.1, orrecirculate its previous value. Picture number can take the previousvalue or the previous value incremented by one (or one plus delta, thedifference between actual and expected temporal reference, in the caseof H.261). This value is supplied by the 8-bit adder present in theblock. The first input to this adder is thispnum, the picture number ofthe data currently being written. TABLE C.2.1 Buffer Status ValuesBuffer Status Value EMPTY 00 FULL 01 READY 10 IN_USE 11

[3025] This needs to be stored separately (in its own master-slavearrangement) so that any of the three buffer picture number registerscan be easily updated based on the current (or previous) picture numberrather than on their own previous picture number (which is almost alwaysout of date). This_pnum is reset to −1 so that when the first picturearrives it is added to the output from the adder and, hence, the inputto the first buffer picture number register, is zero.

[3026] Note that in the current version, delta is connected to zerobecause of the absence of the temporal reference block which shouldsupply the value.

[3027] C.2.3.2.4 Presentation Number

[3028] The 8-bit presentation number register has an associatedpresentation ftlag which is use d in the state machine t o indicate thatthe presentation number has changed since it was last examined. This isnecessary because the picture clock is essentially asynchronous and maybe active during any state, not just those which are concerned with thepresentation number. The rest of the circuitry in this block isconcerned with detecting that a picture clock pulse has occurred and“remembering” this fact. In this way, the presentation number can beupdated at a time when it is valid to do so. A representative sequenceof events is shown in FIG. 156. The signal incr_prn goes active thecycle after the re-timed picture clock rising edge, and persists until astate is entered during which presentation number can be modified. Thisis indicated by the signal en_prnum. The reason for only allowingpresentation number to be updated during certain states is because it isused to drive a significant amount of logic, including a standard-cell,not-very-fast 8-bit adder to provide the signal rdyst. It must,therefore, be changed only during states in which the subsequent statedoes not use the result.

[3029] C.2.3.2.5 Temporal Reference

[3030] The temporal reference block in accordance with the presentinvention, has been omitted from the current embodiment of the ImageFormatter, but its operation is described here for completeness.

[3031] The function of this block is to calculate delta, the differencebetween the temporal reference value received in a token in an H,261data stream, and the “expected” temporal reference (one plus theprevious value). This allows frames to be skipped in H.261. Temporalreference tokens are ignored in all non-H.261 streams. The calculatedvalue is used in the status block to calculate picture numbers for thebuffers. The effect of omitting the block from bmlogic is that picturenumbers will always be sequential in any sequence, even if the H.261stream indicates that some should be skipped.

[3032] The main components of the block (visible in the schematicbm_tref) are registers for tr, exptr and delta. In the invention, tr isreset to zero and loaded, when appropriate, from the input dataregister. Similarly, exptr is reset to −1, and is incremented by either1 or delta during the sequence of temporal reference states. Inaddition, delta is reset to zero and is loaded with the differencebetween the other two registers. All three registers are reset after aFLUSH token. The adder in this block is used for calculation of bothdelta and exptr, i.e., a subtract and an add operation, respectively,and is controlled by the signal delta_calc.

[3033] C.2.3.2.6 Control Resisters (bm urecs)

[3034] Control registers for the buffer manager reside in the blockbm_uregs. These are the access bit register, setup register (definingthe maximum number of external buffers, and internal/external pictureclock), and the target index register. The access bit is synchronized asexpected. The signals stopd_(—)0, stopd_(—)1 and nstopd_(—)1 are derivedform the OR of the access bit and the two event stop bits. Upi addressdecoding for all of bmlogic is done by the block bm_udec, which takesthe lower 4 bits of the upi data bus together with the 2 select signalsfrom the Image Formatter top-level address decode.

[3035] C.2.3.2.7 Controlling State Machine

[3036] The state machine logic originally occupied its own block,bm_state. For code generation reasons, however, it has now beenflattened and resides on sheet 2 of the bmlogic schematic.

[3037] The main sections of this logic are the same. This includes thedecoding, the generation of logic signals for the control of otherbmlogic blocks, and the new state encoding, including the flags from_psand from_fl which are used to select routes through the state machine.There are separate blocks to produce the mux control signals for bm_stusand bm_index.

[3038] Signals in the state machine hardware have been given simplealphabetic names for ease of typing and reference. They are all listedin Table C.2.2, together with the logic expressions which theyrepresent. They also appear as comments in the behavioral M. descriptionof bmlogic (bmlogic.M). TABLE C.2.2 Signal Names Used in the StateMachine Signal Name Logic Expression AST_PRES1.presflg.(bstate==FULL).rdytst.(rdy==0). (ix==max) BST_PRES1.presflg.(bstate==FULL).rdytst.(rdy==0).(ix!=max) CST_PRES1.presflg.(bstate==FULL).rdytst.(rdy!=0) DST_PRES1.presflg.!((bstate==FULL).rdytst).(ix==max) EST_PRES1.presflg.!((bstate==FULL).rdytst).(ix!=max) F ST_PRES1.presflg GST_DRQ.drq_valid.disp_acc.(rdy==0).(disp!=0) PPST_DRQ.drq_valid.disp_acc.(rdy==0).(disp!=0).fromps QQST_DRQ.drq_valid.disp_acc.(rdy==0).(disp!=0)fromfl RR ST_DRQ.drq_valid.disp_acc.(rdy==0).(disp!=0).!(fromps+fromfl) HST_DRQ.drq_valid.disp_acc.(rdy!=0).(disp!=0) IST_DRQ.drq_valid.disp_acc.(rdy!=0).(disp==0) JST_DRQ.drq_valid.disp_acc.(rdy==0).(disp==0).fromps NNST_DRQ.drq_valid.disp_acc.(rdy==0).(disp==0).fromfl OO ST_DRQ.drq_valid.disp_acc.(rdy==0).(disp==0).!(fromps+fromfl) KST_DRQ.!(drq_valid.disp_acc).fromps LLST_DRQ.!(drq_valid.disp_acc).fromfl MMST_DRQ.!(drq_valid.disp_acc).!(fromps+fromfl) L ST_TOKEN.ivr.oar.(idr==TEMPORAL_REFERENCE) SS ST_TOKEN.ivr.oar.(idr==TEMPORAL_REFERENCE).H261 TT ST_TOKEN.ivr.oar.(idr==TEMPORAL_REFERENCE).!H261 M ST_TOKEN.ivr.oar.(idr==FLUSH) NST_TOKEN.ivr.oar.(idr==PICTURE_START) OST_TOKEN.ivr.oar.(idr==PICTURE_END) PST_TOKEN.ivr.oar.(idr==<OTHER_TOKEN>) JJST_TOKEN.ivr.oar.(idr==<OTHER_TOKEN>).in_extn KKST_TOKEN.ivr.oar.(idr==<OTHER_TOKEN>).!in_extn Q ST_TOKEN.!(ivr.oar) SST_PICTURE_END.(ix==arr).!rdytst.oar T ST_PICTURE_END(ix==arr).rdytst.(rdy==0).oar UST_PICTURE_END.(ix==arr).rdytst.(rdy!=0).oar VV ST_PICTURE_END.!oarRorVV ST_PICTURE_END.!((ix==arr).oar) V ST_TEMP_REF0.ivr.oar WST_TEMP_REF0.!(ivr.oar) X ST_OUTPUT_TAIL.ivr.oar FFST_OUTPUT_TAIL.ivr.oar.!in_extn Y ST_OUTPUT_TAIL.!(ivr.oar) GGST_OUTPUT_TAIL.!(ivr.oar).in_extn DD ST_FLUSH.(ix==max).((bstate==VAC)+((bstate==USE).(ix==disp)) Z ST_FLUSH.(ix!=max).((bstate==VAC)+((bstate==USE).(ix==disp)) DDorEE!((bstate==VAC)+((bstate==USE).(ix==disp))+(ix==max) AAST_ALLOC.(bstate==VAC).oar BB ST_ALLOC.(bstate!=VAC).(ix==max) CCST_ALLOC.(bstate!=VAC).(ix!=max) UU ST_ALLOC.!oar

[3039] C.2.3.2.8 Monitorina Operation (bminfo)

[3040] In the present invention, the module, bminfo, is included so thatbuffer status information, index values and presentation number can beobserved during simulations. It is written in M and produces an outputeach time one of its inputs changes.

[3041] C.2.3.3 Register Address Map

[3042] The buffer manager's address space is split into two areas,user-accessible and test. There are, therefore, two separate enablewires derived from range decodes at the top-level. Table C.2.3 shows theuser-accessible registers, and Table C.2.4 shows the contents of thetest space. TABLE C.2.3 User-Accessible Registers Register Name AddressBits Reset State Function BU_BM_ACCESS 0x10 [0] 1 Access bit for buffermanager BU_BM_CTL0 0x11 [0] 1 Max buf lsb. 1→3 buffers.6→2 [1] 1External picture elect select BU_BM_TARGET_IX 0x12 [3:0] 0x0 Fordetecting arrival of picture BU_BM_PRES_NUM 0x13 [7:0] 0x00 Presentationnumber BU_BM_THIS_PNUM 0x14 [7:0] 0xFF Current picture numberBU_BM_PIC_NUM0 0x15 [7:0] none Picture number in buffer 1 BU_BM_PIC_NUM10x16 [7:0] none Picture number in buffer 2 BU_BM_PIC_NUM2 0x17 [7:0]none Picture number in buffer 3 BU_BM_TEMP_REF 0x18 [4:0] 0x00 Temporalreference from stream

[3043] TABLE C.2.4 Test Registers Register Name Address Bits Reset StateFunction BU_BM_PRES_FLAG 0x80 [0] 0 Presentation flag BU_BM_EXP_TR 0x81[4:0] 0xFF Expected temporal reference BU_BM_TR_DELTA 0x82 [4:0] 0x00Delta BU_BM_ARR_IX 0x83 [1:0] 0x0 Arrival buffer index BU_BM_DSP_IX 0x84[1:0] 0x0 Display buffer index BU_BM_RDY_IX 0x85 [1:0] 0x0 Ready bufferindex BU_BM_ESTATE3 0x86 [1:0] 0x0 Buffer 3 status BU_BM_ESTATE2 0x87[1:0] 0x0 Buffer 2 status BU_BM_ESTATE1 0x88 [1:0] 0x0 Buffer 1 statusBU_BM_INDEX 0x89 [1:0] 0x0 Current buffer index BU_BM_STATE 0x8A [4:0]0x00 Buffer manager state BU_BM_FROMPS 0x8B [0] 0x0 From PICTURE_STARTflag BU_BM_FROMFL 0x8C [0] 0x0 From FLUSH_TOKEN flag

[3044] C.2.4 Operation of the State Machine

[3045] There are 19 states in the buffer manager's state machine, asdetailed in Table C.2.5. These interact as shown in FIG. 157, and alsoas described in the behavioral description bmlogic.M. TABLE C.2.5 BufferStates State Value PRES0 0x00 PRES1 0x10 ERROR 0x1F TEMP_REF0 0x04TEMP_REF1 0x05 TEMP_REF2 0x06 TEMP_REF3 0x07 ALLOC 0x03 NEW_EXP_TR 0x0DSET_ARR_IX 0x0E NEW_PIC_NUM 0x0F FLUSH 0x01 DRQ 0x0B TOKEN 0x0COUTPUT_TAIL 0x08 VACATE_RDY 0x17 USE_RDY 0x0A VACATE_DISP 0x09PICTURE_END 0x02

[3046] C.2.4.1 The Reset State

[3047] The reset state is PRESO, with flags set to zero such that themain loop circulated initially.

[3048] C.2.4.2 The Main Loop

[3049] The main loop of the state machine comprises the states shown inFIG. 153 (high-lighted in the main diagram—FIG. 152). States PRES0 andPRES1 are concerned with detecting a picture clock via the signalpresflg. Two cycles are allowed for the tests involved since they alldepend on the value of rdyst, the adder output signal described inC.2.3.2.4. If a presentation flag is detected, all of the buffers areexamined for possible ‘readiness’, otherwise the state machine justadvances to state DRQ. Each cycle around the PRES0-PRES1 loop examines adifferent buffer, checking for full and ready conditions. If these aremet, the previous ready buffer (if one exists) is cleared, the new readybuffer is allocated and its status is updated. This process is repeateduntil all buffers have been examined (index==max buf) and the state thenadvances. A buffer is deemed to be ready for display when any of thefollowing is true: (pic_num>pres_num)&&((pic_num − pres_num)>=128) or(pic_num<pres_num)&&((pres_num − pic_num)<=128) or pic_num == pres_num

[3050] State DRQ checks for a request for a display buffer(drq_vali_dreg && disp_acc_reg). If there is no request the stateadvances (normally to state TOKEN—as will be described later).Otherwise, a display buffer index is issued as follows. If there is noready buffer, the previous index is re-issued or, if there is noprevious display buffer, a null index (zero) is issued. If a buffer isready for display, its index is issued and its state is updated. Ifnecessary, the previous display buffer is cleared. The state machinethen advances as before.

[3051] State TOKEN is the typical option for completing the main loop.If there is valid input and the output is not stalled, tokens areexamined for strategic values (described in later sections), otherwisecontrol returns to state PRESO.

[3052] Control only diverges from the main loop when certain conditionsare met. These are described in the following sections.

[3053] C.2.4.3 Allocating the Ready Buffer Index

[3054] If during the PRES0-PRES1 loop a buffer is determined to beready, any previous ready buffer needs to be vacated because only onebuffer can be designated ready at any time. State VACATE_RDY clears theold ready buffer by setting its state to VACANT, and it resets thebuffer index to 1 so that when control returns to the PRESO state, allbuffers will be tested for readiness. The reason for this is that theindex is by now pointing at the previous ready buffer (for the purposeof clearing it) and there is no record of our intended new ready bufferindex. It is necessary, therefore, to re-test all of the buffers.

[3055] C.2.4.4 Allocating the Display Buffer Index

[3056] Allocation of the display buffer index takes place eitherdirectly from state DRQ (state USER_DY) or via state VACATE_DISP whichclears the old display buffer state. The chosen display buffer isflagged as IN_USE, the value of rdy_buf is set to zero, and the index isreset to 1 to return to state DRQ. Moreover, disp_buf is given therequired index and the two-wire interface wires (disp_valid and drq_acc)are controlled accordingly. Control returns to state DRQ only so thatthe decision between states TOKEN, FLUSH and ALLOC does not need to bemade in state USER_DY.

[3057] C.2.4.5 Operation when PICTURE_END Received

[3058] On receipt of a PICTURE_END token, control transfers from stateTOKEN to state PICTURE_END where, if the index is not already pointingat the current arrival buffer, it is set to point there so that itsstatus can be updated. Assuming both out_acc_reg and en_full are true,status can be updated as described below. If not, control remains instate PICTURE_END until they are both true. The en_full signal issupplied by the write address generator to indicate that the swingbuffer has swung, i.e., the last block has been successfully written andit is, therefore, safe to update the buffer status.

[3059] The just-completed buffer is tested for readiness and given thestatus either FULL or READY depending on the result of the test. If itis ready, rdy_buf is given the value of its index and the set_la_evsignal (late arrival event) is set high (indicating that the expecteddisplay has got ahead in time of the decoding). The new value of arr_bufnow becomes zero and, if the previous ready buffer needs its statusclearing, the index is set to point there and control moves to stateVACATE_RDY. Otherwise, the index is reset to 1 and control returns tothe start of the main loop.

[3060] C.2.4.6 Operation when PICTURE_START Received (Allocation ofArrival Buffer)

[3061] When a PICTURE_START token arrives during state TOKEN, the flagfromps is set, causing the basic state machine loop to be changed suchthat state ALLOC is visited instead of state TOKEN. State ALLOC isconcerned with allocating an arrival buffer (into which the arrivingpicture data can be written), and cycles through the buffers until itfinds one whose status is VACANT. A buffer will only be allocated if outaccreg is high since it is output on the data two-wire interface.Accordingly, cycling around the loop will continue until this is indeedthe case. Once a suitable arrival buffer has been found, the index isallocated to arrbuf and its status is flagged as IN_USE. Index is set to1, the flag fromps is reset, and the state is set to advance toNEW_EXP_TR. A check is made on the picture's index (contained in theword following the PICTURE_START) to determine if it is the same astargix (the target index specified at setup) and, if so, set_if+_ev(index found event) is set high.

[3062] The three states NEW_EXP_TR, SET_ARR_IX and NEW_PIC_NUM set upthe new expected temporal reference and picture number for the incomingdata. The middle state just sets the index to be arr_buf so that thecorrect picture number register is updated (note that this_pnum is alsoupdated). Control then proceeds to state OUTPUT TAIL which outputs data(assuming favorable two-wire interface signals) until a low extension isencountered. At this point, the main loop is re-started. This means thatwhole data blocks (64 items) are output, in between which, there are notests for presentation flags or display requests.

[3063] C.2.4.7 Operation when FLUSH Received

[3064] A FLUSH token in the data stream indicates that sequenceinformation (presentation number, picture number, rstfld) should bereset. This can only occur when all of the data leading up to the FLUSHhas been correctly processed. Accordingly, it is necessary, havingreceived a FLUSH, to monitor the status of all of the buffers until itis certain that all frames have been handed over to the display, i.e.,all but one of the buffers have status EMPTY, and the other is IN_USE(as the display buffer). At that point, a “new sequence” can safely beused.

[3065] When a FLUSH token is detected in state TOKEN, the flag from_flis set, causing the basic state machine loop to be changed such thatstate FLUSH is visited instead of state TOKEN. State FLUSH examines thestatus of each buffer in turn, waiting for it to become VACANT or IN_USEas display. The state machine simply cycles around the loop until thecondition is true, then increments its index and repeats the processuntil all of the buffers have been visited. When the last bufferfulfills the condition, presentation number, picture number, and all ofthe temporal reference registers assume their reset values rst_fld isset to 1. The flag from_fl is reset and the normal main loop operationis resumed.

[3066] C.2.4.8 Operation when TEMPORAL_REFERENCE Received

[3067] When a TEMPORAL_REFERENCE token is encountered, a check is madeon the H.261 bit and, if set, the four states TEMP_REF0 to TEMP_REF3 arevisited. These perform the following operations:

[3068] TEMP_REF0:tempref=in datareg;

[3069] TEMP_REF1:delta=tempref-exptr;index=arrbuf;

[3070] TEMP_REF2:exptr=delta+exptr;

[3071] TEMP_REF3:picnum[i]=thispnum+delta;index=l.

[3072] C.2.4.9 Other Tokens and Tails

[3073] State TOKEN passes control to state OUTPUT_TAIL in all casesother than those outlined above. Control remains here until the lastword of the token is encountered (in_extn_reg is low) and the main loopis then reentered.

[3074] C.2.5 Applications Notes

[3075] C.2.5.1 State Machine Stalling Buffer Manager Input

[3076] This requirement repeatedly check for the “asynchronous” timingevents of picture clock and display buffer request. The necessity ofhaving the buffer manager input stalled during these checks means thatwhen there is a continuous supply of data at the input to the buffermanager, there will be a restriction on the data rate through the buffermanager. A typical sequence of states may be PRESO, PRESl, DRQ, TOKEN,OUTPUT_TAIL, each, with the exception of OUTPUT_TAIL, lasting one cycle.This means that for each block of 64 data items, there will be anoverhead of 3 cycles during which the input is stalled (during statesPRES0, PRES1 and DRQ) thereby slowing the write rate by 3/64 orapproximately 5%. This number may occasionally increase to up to 13cycles of overhead when auxiliary branches of the state machine areexecuted under worst-case conditions. Note that such large overheadswill only apply on a once-per-frame basis.

[3077] C.2.5.2 Presentation Number Behavior During an Access

[3078] The particular embodiment of the bmpres illustrated by theschematic shown in C.2.3.2.4 means that presentation number free-runsduring upi accesses. If presentation number is required to be the samewhen access is relinquished as it was when access was gained, this canbe effected by reading presentation number after access is granted, andwriting it back just before it is relinquished. Note that this isasynchronous, so it may be desirable to repeat the accesses severaltimes to further ensure effectiveness.

[3079] C.2.5.3 H.261 Temporal Reference Numbers

[3080] The module bm_tref (not shown) should be included in the bmlogic.The H.261 temporal reference values are correctly processed by directingdelta input from the bmtref to the bm stus module. The delta input canbe tied to zero if the frames are always sequential.

[3081] SECTION C.3 Write Address Generation

[3082] C.3.1 Introduction

[3083] The function of the write address generation hardware, inaccordance with the present invention, is to produce block addresses fordata to be written away to the buffers. This takes account of bufferbase addresses, the component indicated inthe stream, horizontal andvertical sampling within a macroblock, picture dimensions, and codingstandard. Data arrives in macroblock form, but must be stored so thatlines may be retrieved easily for display.

[3084] C.3.2 Functional Overview

[3085] Each time a new block arrives in the data stream (indicated by aDATA token), the write address generator is required to produce a newblock address. It is not necessary to produce the address immediately,because up to 64 data words can be stored by the DRAM interface (in-theswing buffer) before the address is actually needed. This means that thevarious address components can be added to a running total in successivecycles, and thus, hence obviating the need for any hardware multipliers.The macroblock counter function is effected by storing strategicterminal values and running counts in the register file, these being theoperands for comparisons and conditional updates after each blockaddress calculation.

[3086] Considering the picture format shown in FIG. 161, expectedaddress sequences can be derived for both standard and H.261-like datastreams. These are shown below. Note that the format does not actuallyconform to the H.261 specification because the slices are not wideenough (3 macroblocks rather than 11) but the same“half-picture-width-slice” concept is used here for convenience and thesequence is assumed to be “H.261-type”. Data arrives as fullmacroblocks, 4:2:0 in the example shown, and each component is stored inits own area of the specified buffer.

[3087] Standard address sequence:

[3088] 000,001,00C,00D,100,200;

[3089] 002,003,00E,00F,101,201;

[3090] 004,005,010,011,102,202;

[3091] 006,007,012,013,103,203;

[3092] 008,009,014,015,104,105;

[3093] 00A,00B,016,017,105,205;

[3094] 018,019,024,025,106,107;

[3095]01A.01B,026 . . .

[3096] . . .

[3097] 080,081,08C,080,122,222;

[3098]082,083,08E,08F,123,223;

[3099] H261-type sequence:

[3100] 000,001,00C,00D,100.200;

[3101] 002,003,00E,00F,101,201;

[3102] 004,005,010,011,102,202;

[3103] 018,019,024,025,106,107;

[3104] 01A,01B,026,027,107,207;

[3105] 01C,01D,028,029,108,208;

[3106] 030,031,03C,03D,10C,20C,

[3107] 032,033,03E,03F,10D,20D;

[3108] 034,035,040,041,10E,20E;

[3109] 006,007,012,013,103,203;

[3110] 008,009,014,015,104,105;

[3111] 00A,00B,016,017,105,205;

[3112] 01E,01F,02A,02B,109,209;

[3113] 020,021 ,02C,02D,10A,20A;

[3114] 022,023,02E,02F, 10B,20B;

[3115] 036,037,042,043,10F,20F;

[3116] 038,039,044,045,110,210;

[3117] C3A,03B,046,047,111,211;

[3118] 048,049,054,055,112,212;

[3119] 04A,04B,056 . . .

[3120] . . .

[3121] 06A,06B,076,077,11D,21D;

[3122] 07E,07F,08A,08B,121,221;

[3123] 080,081,08C,08D,122,222;

[3124] 082,083,08E,08F,123:223;

[3125] C.3.3 Architecture

[3126] C.3.3.1 Interfaces

[3127] C.3.3.1.1 Interface to Buffer Manager

[3128] The buffer manager outputs data and the buffer index directly tothe write address generator. This is performed under the control of atwo-wire-interface. In some ways, it is possible to consider the writeaddress generator block as an extension of the buffer manager becausethe two are very closely linked. They do, however, operate from twoseparate (but similar) clock generators.

[3129] C.3.3.1.2 Interface to Dramif

[3130] The write address generator provides data and addresses for theDRAM interface. Each of these has their own two-wire-interface, and thedramif uses each of them in different clock regimes. In particular, theaddress is clocked into the dramif on a clock which is not related tothe write address generator clock. It is, therefore, synchronized at theoutput.

[3131] C.3.3.1.3 Microprocessor Interface

[3132] The write address generator uses three bits of microprocessoraddress space together with 8-bit data bus and read and write strobes.There is a single select bit for register access.

[3133] C.3.3.1.4 Events

[3134] The write address generator is capable of producing fivedifferent events. Two are in response to picture size informationappearing in the data stream (hmbs and vmbs) and three are in responseto DEFINE SAMPLING tokens (one event for each component.

[3135] C.3.3.2 Basic Structure

[3136] The structure of the write address generator is shown in theschematic waddrgen.sch. It comprises a datapath, some controlling logic,and snoopers and synchronization.

[3137] C.3.3.2.1 The Datapath (bwadpath)

[3138] The datapath is of the type described in Chapter C.5 of thisdocument, comprising an 18-bit adder/subtractor and register file (seeC.3.3.4), and producing a zero flag (based on the adder output) for usein the control logic.

[3139] C.3.3.2.2 The Controlling Logic

[3140] The controlling logic of the present invention consists ofhardware to generate all of the register file load and drive signals,the adder control signals, the two-wire-interface signals, and alsoincludes the writable control registers.

[3141] C.3.3.2.3 Snoopers and Synchronization

[3142] Super snoopers exist on both the data and address ports. Snoopersin the datapaths, controlled as super-snoopers from the zcells. Theaddress has synchronization between the write address generator clockand the dramif's “clk” regime. Syncifs are used in the zcells for thetwo-wire interface signals, and simplified synchronizers are used in thedatapath for the address.

[3143] C.3.3.3 Controlling Logic and State Machine

[3144] C.3.3.3.1 Input/Output Block (wa inout)

[3145] This block contains the input and two output two-wire interfaces,together with latches for the input data (for token decode) and arrivalbuffer index (for decoding four ways).

[3146] C.3.3.3.2 Two Cycle Control Block (wa fc)

[3147] The flag fc (first cycle) is maintained here and indicateswhether the state machine is in the middle of a two-cycle operation(i.e., an operation involving an add).

[3148] C.3.3.3.3. Component Count (wa comp)

[3149] Separate addresses are required for data blocks in eachcomponent, and this block maintains the current component underconsideration based on the type of DATA header received in the inputstream.

[3150] C.3.3.3.4 Modulo-3 Control (wa mod3)

[3151] When generating address sequences for H.261 data streams, it isnecessary to count three rows of macroblocks to half way along thescreen (see C.3.2). This is effected by maintaining a modulo-3 counter,incremented each time a new row of macroblocks is visited.

[3152] C.3.3.3.5 Control Registers (wa uregs)

[3153] Module wa_uregs contains the setup register and the codingstandard register—the latter is loaded from the data stream. The setupregister uses 3 bits: QCIF (lsb) and the maximum component expected inthe data stream (bits 1 and 2). The access bit also resides in thisblock (synchronized as usual), with the “stopped” bits being derived atthe next level up the hierarchy (walogic) as the OR of the access bitand the event stop bits. Microprocessor address decoding is done by theblock wa_udec which takes read and write strobes, a select wire, and thelower two bits of the address bus.

[3154] C.3.3.3.6 Controlling State Machine (wa state)

[3155] The logic in this block is split into several distinct areas. Thesate decode, new state encode, derivation of “intermediate” logicsignals, datapath control signals (drivea, driveb, load, adder controlsand select signals), multiplexer controls, two-wire-interface controls,and the five event signals.

[3156] C.3.3.3.7 Event Generation

[3157] The five event bits are generated as a result of certain tokensarriving at the input. It is important that, in each case, the entiretoken is received before any events are generated because the eventservice routines perform calculations based on the new values received.For this reason, each of the bits is delayed by a whole cycle beforebeing input to the event hardware

[3158] C.3.3.4 Register Address Map

[3159] There are two sets of registers in the write address generatorblock. These are the top-level setup type registers located in thestandard cell section, and keyholed datapath registers. These are listedin Table C.3.1 and C.3.2, respectively. TABLE C.3.1 Top-Level RegistersReset Register Name Address Bits State Function BU_WADDR_COD_STD 0x4 2 0Cod std from data stream BU_WADDR_ACCESS 0x5 1 0 Access bitBU_WADDR_CTL1 0x6 3 0 max component[2:1] and CCIF[0] BU_WA_ADDR_SNP20xB0 8 snooper on the write BU_WA_ADDR_SNP1 0xB1 8 address generatorBU_WA_ADDR_SNP0 0xB2 8 address c/p. BU_WA_DATA_SNP1 0xB4 8 snooper ondata output of BU_WA_DATA_SNP0 0xB5 8 WA

[3160] TABLE C.3.2 Image Formatter Address Generator Keyhole KeyholeKeyhole Register Name Address Bits Comments BU_WADDR_BUFFER0_BASE_MSB0x85 2 Must be BU_WADDR_BUFFER0_BASE_MID 0x86 8 LoadedBU_WADDR_BUFFER0_BASE_LSB 0x87 8 BU_WADDR_BUFFER1_BASE_MSB 0x89 2 Mustbe BU_WADDR_BUFFER1_BASE_MID 0x8a 8 Loaded BU_WADDR_BUFFER1_BASE_LSB0x8b 8 BU_WADDR_BUFFER2_BASE_MSB 0x8d 2 Must beBU_WADDR_BUFFER2_BASE_MID 0x8e 8 Loaded BU_WADDR_BUFFER2_BASE_LSB 0x8f 8BU_WADDR_COMP0_HMBADDR_MSB 0x91 2 Test only BU_WADDR_COMP0_HMBADDR_MID0x92 8 BU_WADDR_COMP0_HMBADDR_LSB 0x93 8 BU_WADDR_COMP1_HMBADDR_MSB 0x952 Test only BU_WADDR_COMP1_HMBADDR_MID 0x96 8 BU_WADDR_COMP1_HMBADDR_LSB0x97 8 BU_WADDR_COMP2_HMBADDR_MSB 0x99 2 Test onlyBU_WADDR_COMP2_HMBADDR_MID 0x9a 8 BU_WADDR_COMP2_HMBADDR_LSB 0x9b 8BU_WADDR_COMP0_VMBADDR_MSB 0x9d 2 Test only BU_WADDR_COMP0_VMBADDR_MID0x9e 8 BU_WADDR_COMP0_VMBADDR_LSB 0x9f 8 BU_WADDR_COMP1_VMBADDR_MSB 0xa12 Test only BU_WADDR_COMP1_VMBADDR_MID 0xa2 8 BU_WADDR_COMP1_VMBADDR_LSB0xa3 8 BU_WADDR_COMP2_VMBADDR_MSB 0xa5 2 Test onlyBU_WADDR_COMP2_VMBADDR_MID 0xa6 8 BU_WADDR_COMP2_VMBADDR_LSB 0xa7 8BU_WADDR_VBADDR_MSB 0xa9 2 Test only BU_WADDR_VBADDR_MID 0xaa 8BU_WADDR_VBADDR_LSB 0xab 8 BU_WADDR_COMP0_HALF_WIDTH_IN_BLOCKS_MSB 0xad2 Must be BU_WADDR_COMP0_HALF_WIDTH_IN_BLOCKS_MID 0xae 8 LoadedBU_WADDR_COMP0_HALF_WIDTH_IN_BLOCKS_LSB 0xaf 8BU_WADDR_COMP1_HALF_WIDTH_IN_BLOCKS_MSB 0xb1 2 Must beBU_WADDR_COMP1_HALF_WIDTH_IN_BLOCKS_MID 0xb2 8 LoadedBU_WADDR_COMP1_HALF_WIDTH_IN_BLOCKS_LSB 0xb3 8BU_WADDR_COMP2_HALF_WIDTH_IN_BLOCKS_MSB 0xb5 2 Must beBU_WADDR_COMP2_HALF_WIDTH_IN_BLOCKS_MID 0xb6 8 LoadedBU_WADDR_COMP2_HALF_WIDTH_IN_BLOCKS_LSB 0xb7 8 BU_WADDR_HB_MSB 0xb9 2Test only BU_WADDR_HB_MID 0xba 8 BU_WADDR_HB_LSB 0xbb 8BU_WADDR_COMP0_OFFSET_MSB 0xbd 2 Must be BU_WADDR_COMP0_OFFSET_MID 0xbe8 Loaded BU_WADDR_COMP0_OFFSET_LSB 0xbf 8 BU_WADDR_COMP1_OFFSET_MSB 0xc12 Must be BU_WADDR_COMP1_OFFSET_MID 0xc2 8 LoadedBU_WADDR_COMP1_OFFSET_LSB 0xc3 8 BU_WADDR_COMP2_OFFSET_MSB 0xc5 2 Mustbe BU_WADDR_COMP2_OFFSET_MID 0xc6 8 Loaded BU_WADDR_COMP2_OFFSET_LSB0xc7 8 BU_WADDR_SCRATCH_MSB 0xc9 2 Test only BU_WADDR_SCRATCH_MID 0xca 8BU_WADDR_SCRATCH_LSB 0xcb 8 BU_WADDR_MBS_WIDE_MSB 0xcd 2 Must beBU_WADDR_MBS_WIDE_MID 0xce 8 Loaded BU_WADDR_MBS_WIDE_LSB 0xcf 8BU_WADDR_MBS_HIGH_MSB 0xd1 2 Must be BU_WADDR_MBS_HIGH_MID 0xd2 8 LoadedBU_WADDR_MBS_HIGH_LSB 0xd3 8 BU_WADDR_COMP0_LAST_MB_IN_ROW_MSB 0xd5 2Must be BU_WADDR_COMP0_LAST_MB_IN_ROW_MID 0xd6 8 LoadedBU_WADDR_COMP0_LAST_MB_IN_ROW_LSB 0xd7 8BU_WADDR_COMP1_LAST_MB_IN_ROW_MSB 0xd9 2 Must beBU_WADDR_COMP1_LAST_MB_IN_ROW_MID 0xda 8 LoadedBU_WADDR_COMP1_LAST_MB_IN_ROW_LSB 0xdb 8BU_WADDR_COMP2_LAST_MB_IN_ROW_MSB 0xdd 2 Must beBU_WADDR_COMP2_LAST_MB_IN_ROW_MID 0xde 8 LoadedBU_WADDR_COMP2_LAST_MB_IN_ROW_LSB 0xdf 8BU_WADDR_COMP0_LAST_MB_IN_HALF_ROW_MSB 0xe1 2 Must beBU_WADDR_COMP0_LAST_MB_IN_HALF_ROW_MID 0xe2 8 LoadedBU_WADDR_COMP0_LAST_MB_IN_HALF_ROW_LSB 0xe3 8BU_WADDR_COMP1_LAST_MB_IN_HALF_ROW_MSB 0xe5 2 Must beBU_WADDR_COMP1_LAST_MB_IN_HALF_ROW_MID 0xe6 8 LoadedBU_WADDR_COMP1_LAST_MB_IN_HALF_ROW_LSB 0xe7 8BU_WADDR_COMP2_LAST_MB_IN_HALF_ROW_MSB 0xe9 2 Must beBU_WADDR_COMP2_LAST_MB_IN_HALF_ROW_MID 0xea 8 LoadedBU_WADDR_COMP2_LAST_MB_IN_HALF_ROW_LSB 0xeb 8BU_WADDR_COMP0_LAST_ROW_IN_MB_MSB 0xed 2 Must beBU_WADDR_COMP0_LAST_ROW_IN_MB_MID 0xee 8 LoadedBU_WADDR_COMP0_LAST_ROW_IN_MB_LSB 0xef 8BU_WADDR_COMP1_LAST_ROW_IN_MB_MSB 0xf1 2 Must beBU_WADDR_COMP1_LAST_ROW_IN_MB_MID 0xf2 8 LoadedBU_WADDR_COMP1_LAST_ROW_IN_MB_LSB 0xf3 8BU_WADDR_COMP2_LAST_ROW_IN_MB_MSB 0xf5 2 Must beBU_WADDR_COMP2_LAST_ROW_IN_MB_MID 0xf6 8 LoadedBU_WADDR_COMP2_LAST_ROW_IN_MB_LSB 0xf7 8BU_WADDR_COMP0_BLOCKS_PER_MB_ROW_MSB 0xf9 2 Must beBU_WADDR_COMP0_BLOCKS_PER_MB_ROW_MID 0xfa 8 LoadedBU_WADDR_COMP0_BLOCKS_PER_MB_ROW_LSB 0xfb 8BU_WADDR_COMP1_BLOCKS_PER_MB_ROW_MSB 0xfd 2 Must beBU_WADDR_COMP1_BLOCKS_PER_MB_ROW_MID 0xfe 8 LoadedBU_WADDR_COMP1_BLOCKS_PER_MB_ROW_LSB 0xff 8BU_WADDR_COMP2_BLOCKS_PER_MB_ROW_MSB 0x101 2 Must beBU_WADDR_COMP2_BLOCKS_PER_MB_ROW_MID 0x102 8 LoadedBU_WADDR_COMP2_BLOCKS_PER_MB_ROW_LSB 0x103 8BU_WADDR_COMP0_LAST_MB_ROW_MSB 0x105 2 Must beBU_WADDR_COMP0_LAST_MB_ROW_MID 0x106 8 LoadedBU_WADDR_COMP0_LAST_MB_ROW_LSB 0x107 8 BU_WADDR_COMP1_LAST_MB_ROW_MSB0x109 2 Must be BU_WADDR_COMP1_LAST_MB_ROW_MID 0x10a 8 LoadedBU_WADDR_COMP1_LAST_MB_ROW_LSB 0x10b 8 BU_WADDR_COMP2_LAST_MB_ROW_MSB0x10d 2 Must be BU_WADDR_COMP2_LAST_MB_ROW_MID 0x10e 8 LoadedBU_WADDR_COMP2_LAST_MB_ROW_LSB 0x10f 8 BU_WADDR_COMP0_HBS_MSB 0x111 2Must be BU_WADDR_COMP0_HBS_MID 0x112 8 Loaded BU_WADDR_COMP0_HBS_LSB0x113 8 BU_WADDR_COMP1_HBS_MSB 0x115 2 Must be BU_WADDR_COMP1_HBS_MID0x116 8 Loaded BU_WADDR_COMP1_HBS_LSB 0x117 8 BU_WADDR_COMP2_HBS_MSB0x119 2 Must be BU_WADDR_COMP2_HBS_MID 0x11a 8 LoadedBU_WADDR_COMP2_HBS_LSB 0x11b 8 BU_WADDR_COMP0_MAXHB 0x11f 2 Must beBU_WADDR_COMP1_MAXHB 0x123 2 Loaded BU_WADDR_COMP2_MAXHB 0x127 2BU_WADDR_COMP0_MAXVB 0x12b 2 Must be BU_WADDR_COMP1_MAXVB 0x12f 2 LoadedBU_WADDR_COMP2_MAXVB 0x133 2

[3161] The keyhole registers fall broadly into two categories. Thosewhich must be loaded with picture size parameters prior to any addresscalculation, and those which contain running totals of various(horizontal and vertical) block and macroblock counts. The picture sizeparameters may be loaded in response to any of the interrupts generatedby the write address generator, i.e., when any of the picture size orsampling tokens appear in the data stream. Alternatively, if the picturesize is known prior to receiving the data stream, they can be writtenjust after reset. Example setups are given in Sectionr C.13, and thepicture size parameter registers are defined in the next section.

[3162] C.3.4 Programaing the Write Address Generator

[3163] The following datapath registers must contain the correct picturesize information before address calculation can proceed. They areillustrated in FIG. 162.

[3164] 1)WADDR_HALF_WIDTH_IN_BLOCKS: this defines the half width, inblocks, of the incoming picture.

[3165] 2)WADDR_MBS_WIDE: this defines the width, in macroblocks, of theincoming picture.

[3166] 3)WADDR_MBS_HIGH: this defines the height, in macroblocks, of theincoming picture.

[3167] 4)WADDR_LAST_MB_IN_ROW: this defines the block number of the topleft hand block of the last macroblock in a single, full-width row ofmacroblocks. block numbering starts at zero in the top left corner ofthe left-most macroblock, increases across the frame with each block andsubsequently with each following row of blocks within the macroblockrow.

[3168] 5)WADDR_LAST_MB_IN_HALF_ROW: this is similar to the previousitem, but defines the block number of the top left block in the lastmacroblock in a half-width row of macroblocks.

[3169] 6)WADDR_LAST_ROW_IN_MB: this defines the block number of the leftmost block in the last row of blocks within a row of macroblocks.

[3170] 7)WADDR_BLOCKS_PER_MB_ROW: this defines the total number ofblocks contained in a single, full-width row of macroblocks.

[3171] 8)WADDR_LAST_MB_ROW: this defines the top left block address ofthe left-most macroblock in the last row of macroblocks in the picture.

[3172] 9)WADDR_HBS: this defines the width in blocks of the incomingpicture.

[3173] 10)WADDR_MAX_HB: this defines the block number of the right-mostblock in a row of blocks in a single macroblock.

[3174] 11)WADDR_MAXVB: this defines the height-l, in blocks, of a singlemacroblock.

[3175] In addition, the registers defining the organization of the DRAMmust be programmed. These are the three buffer base registers, and the ncomponent offset registers, where n is the number of components expectedin the data stream (it can be defined in the data stream- and can be 1minimum and 3 maximum).

[3176] Note that many of the parameters specify block numbers or blockaddresses. This is because the final address is expected to be a blockaddress, and the calculation is based on a cumulative algorithm.

[3177] The screen configuration illustrated in FIG. 162 yields thefollowing register values:  1)WADDR_HALF_WIDTH_IN_BLOCKS = 0x16 2)WADDR_MBS_WIDE = 0x16  3)WADDR_MBS_HIGH = 0x12 4)WADDR_LAST_MB_IN_ROW = 0x2A  5)WAODR_LAST_MB_IN_HALF_ROW = 0x14 6)WAODR_LAST_ROW_IN_MB = 0x2C  7)WADDR_BLOCKS_PER_MB_ROW = 0x5B 8)WADDR_LAST_MB_ROW = 0x5D8  9)WADDR_HBS = 0x2C 10)WADDR_MAXVB = 111)WADDR_MAXHB = 1

[3178] C.3.5 Operation of the State Machine

[3179] There are 19 states in the buffer manager's state machine, asdetailed in Table C.3.3. These interact as shown in FIG. 164, and alsoas described in the behavioral description, bmlogic.M. TABLE C.3.3 WriteAddress Generator States State Value IDLE 0x00 DATA 0x10 CODING_STANDARD0x0C HORZ_MBS0 0x07 HORZ_MBS1 0x06 VERT_MBS0 0x0B VERT_MBS1 0x0AOUTPUT_TAIL 0x08 HB 0x11 MB0 0x1D MB1 0x12 MB2 0x1E MB3 0x13 MB4 0x0EMB5 0x14 MB6 0x15 MB4A 0x18 MB4B 0x09 MB4C 0x17 MB4D 0x16 ADDR1 0x19ADDR2 0x1A ADDR3 0x1B ADDR4 0x1C ADDR5 0x03 HSAMP 0x05 VSAMP 0x04PIC_ST1 0x0f PIC_ST2 0x01 PIC_ST3 0x02

[3180] C.3.5.1 Calculation of the Address

[3181] The major section of the write address generator state machine isillustrated down the left hand side of FIG. 164. On receipt of a DATAtoken, the state machine moves from state IDLE to state ADDR1 and thenthrough to state ADDR5, from which an 18-bit block address is outputwith two-wire-interface controls. The calculations performed by thestates ADDR1 through to ADDR5 are:

[3182] BU_WADDR_SCRATCH=BU_BUFFERn_BASE+BU_COMPm_OFFSET;

[3183] BU_WADDR_SCRATCH=BU_WADDR_SCRATCH+BU_WADDR_VMBADDR;

[3184] BU_WADDR_SCRATCH=BU_WADDR-SCRATCH+BU_WADDR_HMBADDR;

[3185] BU_WADDR_SCRATCH=BU+_WADDR_SCRATCH+BU_WADDR_VBADDR;

[3186] out_addr=BU_WADDR_SCRATCH+BU_WADDR_HB;

[3187] The registers used are defined as follows:

[3188] 1) BU_WADDR_VMBADDR: the block address (the top left block) ofthe left-most macroblock of the row of macroblocks in which the blockwhose address is being calculated is contained.

[3189] 2) BU_WADDR_HMBADDR: the block address (top left block) of thetop macroblock of the column of macroblocks in which the block whoseaddress is being calculated is contained.

[3190] 3) BU_WADDR_VBADDR: the block address, within the macroblock row,of the left-most block of the row of blocks in which the block whoseaddress is being calculated is contained.

[3191] 4) BU_WADD_RHB: the horizontal block number, within themacroblock, of the block whose address is being calculated.

[3192] 5) BU_WADDR_SCRATCH: the scratch register used for temporarystorage of intermediate results.

[3193] Considering FIG. 163, and taking, for example, the calculation ofthe block whose address is 0×62D, the following sequence of calculationswill take place;

[3194] SCRATCH=BUFFERn_BASE+COMPm_OFFSET; (assume 0)

[3195] SCRATCH=0+0×5D8;

[3196] SCRATCH=0×5D8+0×28;

[3197] SCRATCH=0×600+0×2C;

[3198] block address=0×62C+1=0×62D;

[3199] The contents of the various registers are illustrated in theFigure.

[3200] C.3.5.2 Calculation of New Screen Location Parameters

[3201] When the address has been output, the state machine continues toperform calculations in order to update the various screen locationparameters described above. The states HB and MBO through to MB6 do thecalculations, transferring control at some point to state DATA fromwhich the reminder of the DATA Token is output.

[3202] These states proceed in pairs, the first of a pair calculatingthe difference between the current count and its terminal value and,hence, generating a zero flag. The second of the pair either resets theregister or adds a fixed (based on values in the setup registers derivedfrom screen size) offset. In each case, if the count under considerationhas reached its terminal value (i.e., the zero flag is set), controlcontinues down the “MB” sequence of states. If not, all counts aredeemed to be correct (ready for the next address calculation) andcontrol transfers to state DATA.

[3203] Note that all states which involve the use of an addition orsubtraction take two cycles to complete (allowing the use of a standard,ripple-carry adder), this being effected by the use of a flag, fc (firstcycle) which alternates between 1 and 0 for adder-based states.

[3204] All of the address calculation and screen location calculationstates allow data to be output assuming favorable two-wire interfaceconditions.

[3205] C.3.5*2.l Calculations for Standard (MPEG-style) Sequences

[3206] The sequence of operations is as follows (in which the zero flagis based on the output of the adder): states HB and MBO: scratch = hb −maxhb; if (z) hb = 0; else ( hb = hb + 1 new_state = DATA; ) states MB1and MB2: scratch = vb_addr − last_row_in_mb; if (z) vb_addr = 0; else (vb_addr = vb_addr + width_in_blocks; new_state = DATA; ) states MB3 andMB4: scratch = hmb_addr − last_mb_in_row; if (z) hmb_addr = 0; else (hmb_addr = hmb_addr + maxhb; new_state = DATA; ) states MB5 and MB6:scratch = vmb_addr − last_mb_row; if (!z) vmb_addr = vmb_addr +blocks_per_mb_row; (vmb_addr is reset after a PICTURE_START token isdetected, rather than when the end of a picture is inferred from thecalculations)

[3207] C.3.5.2.2 Calculations for H.261 Sequences

[3208] The sequence for H.261 calculations diverges from the standardsequence at state MB4: states HB and MB0:-as above states MB1 andMB2:-as above states MB3 and MB4: scratch = hmb_addr − last_mb_in_row;if (z & (mod3==2)) /*end of slice on right of screen*/ { hmb_addr − 0;new_state − MB5; } else if (z) /*end of row on right of screen*/ {hmb_addr = half_width_in_blocks; new state = MB4A; } else { scratch =hmb_addr − last_mb_in_half_row; new-state = MB4B; } State MB4A: vmb_addr= vmb_addr + blocks_per_mb_row; new_state = DATA; state(MB4) and MB4B:(scratch = hmb_addr − last_mb_in_half_row;) if (z & (mod3==2)) /*end ofslice on left of screen*/ { hmb_addr = hmb_addr + maxhb; new_state =MB4C; } else if (z) /*end of row on left of screen*/ { hmb_addr = 0;new_state = MB4A; } else { hmb_addr = hmb_addr + maxhb; new_state =DATA; } states MB4C and MB4D: vmb_addr = vmb_addr − blocks_per_mb_row;vmb_addr = vmb_addr − blocks_per_mb_row; new_state = DATA; states MB5and MB6:-as above

[3209] C.3.5.3 Operation on PICTURE_START Token

[3210] When a PICTURE_START token is received, control passes to statePIC_ST1 where the vb_addr register (BU_WADDR_VBADDR) is reset to 0. Eachof states PIC_ST2 and PIC_ST3 are then visited, once for each component,resetting hmb_addr and vmb_addr respectivey. Control then returns, viastate OUTPUT_TAIL. to IDLE.

[3211] C.3.5.3 Operation on PICTURE_START Token

[3212] When a PICTURE_START token is received, control passes to statePIC_ST1 where the vbaddr register (BU_WADDR_VBADDR) is reset to 0. Eachof states PIC_ST2 and PIC_ST3 are then visited, once for each component,resetting hmb_addr and vmb_addr, respectively. Control then returns, viastate OUTPUT_TAIL, to IDLE.

[3213] C.3.5.4 Operation on DEFINE_SAMPLING Token

[3214] When a DEFINE_SAMPLING token is received, the component registeris loaded with the least significant two bits of the input data. Inaddition, via states HSAMP and VSAMP, the maxhb and maxvb registers forthat component are loaded. Furthermore, the appropriate define samplingevent bit is triggered (delayed by one cycle to allow the whole token tobe written).

[3215] C.3.5.5 Operation on HORIZONTAL_MBS and VERTICAL_MBS

[3216] When each of HORIZONTAL_MBS and VERTICAL_MBS arrive, the 14-bitvalue contained in the token is written, in two cycles, to theappropriate register. The relevant event bit is triggered, delayed byone cycle.

[3217] C.3.5.6 Other Tokens

[3218] The CODING_STANDARD token is detected and causes the top-levelBU_WADDR_COD_STD register to be written with the input data. This isdecoded and the nh261 flag (not H261) is hardwired to the buffer managerblock. All other tokens cause control to move to state OUTPUT_TAIL,which accepts data until the token finishes. Note, however, that it doesnot actually output any data.

[3219] SECTION C.4 Read Address Generator

[3220] C.4.1 Overview

[3221] The read address generator of the present invention consists offour state machine/datapath blocks. The first, “dline”, generates lineaddresses-and distributes them to the other three (one for eachcomponent) identical page/block address generators, “dramctls”. Allblocks are linked by two wire interfaces. The modes of operation includeall combinations of interlaced/progressive, first field upper/lower, andframe start on upper/lower/both. The Table C.3.4 shows the names,addresses, and reset states of the dispaddr control registers, andChapter C.13 gives a programming example for both address generators.

[3222] C.4.2 Line Address Generator (dline)

[3223] This block calculates the line start addresses for eachcomponent. Table C.3.4 shows the 18 bit datapath registers in dline.

[3224] Note the distinction between DISP_register_name andADDR_register_name DISP_name registers are in dispaddr only and meansthat the register is specific to the display area to be read out of theDRAM. ADDR_name means that the register describes something about thestructure of the external buffers.

[3225] Operation

[3226] The basic operation of dline, ignoring all modes repeats etc. is:if (vsync_start)/* first active cycle of vsync*/ ( comp = 0DISP_VB_CNT_COMP[comp]=0; LINE[comp]=BUFFER_BASE[comp]+0;LINE[comp]=LINE[comp]+DISP_COMP_OFFSET[comp]; while(VB_CNT_COMP[comp]<DISP_VBS_COMP[comp] ( while (line_count[comp]<8) ( (while (comp<3) ( →OUTPUT LINE [comp]to dramctl[comp]line[comp]=LINE[comp]+ADDR_HBS_COMP[comp]; comp = comp + 1;line_count[comp]=line_count[comp]+1; )VB_CNT_COMP[comp]=VB_CNT_COMP[comp]+1; line_count[comp]==0; ) )

[3227] TABLE C.3.4 Dispaddr Datapath Registers Keyhole Register NamesBus Address Description Comments BUFFER_BASE0 A 0x00,01,02,03 Blockaddress These registers BUFFER_BASE1 A 0x04,05,06,07 of the start ofmust be loaded BUFFER_BASE2 A 0x08,09,0a,0b each buffer. by the upibefore DISP_COMP_OFFSET0 B 0x24,25,26,27 Offsets from the operation canDISP_COMP_OFFSET1 B 0x29,29,2a,2b buffer base to begin.DISP_COMP_OFFSET2 B 0x2c,2d,2e,2f where reading begins. DISP_VBS_COMP0 B0x30,31,32,33 Number of DISP_VBS_COMP1 B 0x34,35,36,37 vertical blocksDISP_VBS_COMP2 B 0x38,39,3a,3b to be read ADDR_HBS_COMP0 B 0x3c,3d,3e,3fNumber of ADDR_HBS_COMP1 B 0x40,41,42,43 horizontal ADDR_HBS_COMP2 B0x44,45,46,4 blocks IN THE DATA LINE0 A 0x0c,0d,0e,0f Current line Theseregisters LINE1 A 0x10,11,12,13 address are temporary LINE2 A0x14,15,16,17 locations used DISP_VB_CNT_COMP0 A 0x18,19,1a,1b Number ofby dispaddr. DISP_VB_CNT_COMP1 A 0x1c,1d,1e,1f vertical blocks Note: AllDISP_VB_CNT_COMP2 A 0x20,21,22,23 remaining to be registers are Pj read.W from the upi

[3228] C.4.3 Dline Control Registers

[3229] The above operation is modified by the dispaddr control registerswhich are shown in the Table C.4.3 below. TABLE C.4.3 CONTROL REGISTERSReset Register Name Address Bits State Function LINE_IN_LAST_ROW0 0x08[2:0] 0x07 These three registers LINES_IN_LAST_ROW1 0x09 [2:0] 0x07determine the number of LINES_IN_LAST_ROW2 0x0a [2:0] 0x07 lines (out of8) of the last row of blocks to read out DISPADDR_ACCESS 0x0b [0] 0x00Access bit for dispaddr DISPADDR_CTL0 0x0c [1:0] 0x0 SYNC_MODE See belowfor a detailed [2] 0x0 READ_START description of these [3] 0x1INTERLACED/ PROG control bits [4] 0x0 LSB_INVERT [7:5] 0x0 LINE_RPTDISPADDR_CTL1 0x0d [0] 0x1 COMP0HOLD

[3230] C.4.3.1 LINES_IN LAST_ROW_[component]

[3231] These three registers determine, for each component, the numberof lines in the last row of blocks that are to be read. Thus, the heightof the read window may be an arbitrary number of lines. This is aback-up feature since the top, left and right edges of the window are onblock boundaries, and the output controller can clip (discard) excesslines.

[3232] C.4.3.2 DISPADDR_ACCESS

[3233] This is the access bit for the whole of dispaddr. On writing a“1” to this location, dispaddr is halted synchronously to the clocks.The value read back from the access bit will remain “0” until dispaddrhas safely halted. Having reached this state, it is safe to performasynchronous upi accesses to all the dispaddr registers. Note that theupi is actively locked out from the datapath registers until the accessbit is “1”. In order for access to dispaddr to be achieved withoutdisrupting the current display or datapath operation, access will onlygiven and released under the following circumstances.

[3234] Stopping: Access will only be granted if the datapath hasfinished its current two cycle operation (if it were doing one), and the“safe” signal from the output controller is high. This signal representsthe area on the screen below the display window and is programmed in theoutput controller (not dispaddr). Note: It is, therefore, necessary toprogram the output controller before trying to gain access to dispaddr.

[3235] Starting-Access will only be released when “safe” is high, orduring vsync. This ensures that display will not start too close to theactive window.

[3236] This scheme allows the controlling software to request access,poll until end of display, modify dispaddr, and release access. If thesoftware is too slow and doesn't release the access bit until aftervsync, dispaddr will not start until the next safe period. Border colorwill be displayed during this “lost” picture (rather than rubbish)

[3237] C.4.3.3 DISPADDR_CTLO[7:0]

[3238] When reading the following descriptions, it is important tounderstand the distinction between interlaced data and an interlaceddisplay.

[3239] Interlaced data can be of two forms. The Top-Level Registerssupports field-pictures (each buffer contains one field), and frames(each buffer contains an entire frame—interlaced or not)

[3240] DISPADDR_CTLO[7:0]contains the following control bits:

[3241] SYNC_MODE[1:0)

[3242] With an interlaced display, vsyncs referring to top and bottomfields are differentiated by the field_info pin. In this context,field_info=HIGH meaning the top field. These two control bits determinewhich vsyncs dispaddr will request a new display buffer from the buffermanager and, thus, synchronize the fields in the buffers (if the datawere interlaced) with the fields on the display:

[3243] 0:New Display Buffer On Top Field

[3244] 1:Bottom Field

[3245] 2:Both Fields

[3246] 3:Both Fields

[3247] At startup, dispaddr will request a buffer from the buffermanager on every vsync. Until a buffer is ready, dispaddr will receive azero (no display) buffer. When it finally gets a good buffer index,dispaddr has no idea where it is on the display. It may, therefore, benecessary to synchronize the display startup with the correct vsync.

[3248] READ_START

[3249] For interlaced displays at startup, this bit determines on whichvsync display will actually start. Furthermore, having received adisplay buffer index, dispaddr may “sit out” the current vsync in orderto line up fields on the display with the fields in the buffer.

[3250] INTERLACED/PROGRESSIVE

[3251] 0:Progressive

[3252] 1:Interlaced

[3253] In progressive mode, all lines are read out of the display areaof the buffer. In interlaced mode, only alternate lines are read.Whether reading starts on the first or second line depends onfield_info. Note that with (interlaced) field-pictures, the system wantsto read all lines from each buffer so the setting of this bit would beprogressive. The mapping between field_info and first/second line startmay be inverted by lsb_invert (so named for historical reasons).

[3254] LSB_INVERT

[3255] When set, this bit inverts the field_info signal seen by the linecounter. Thus, reading may be started on the correct line of a frame andaligned to the display regardless of the convention adopted by theencoder, the display or the Top-Level Registers.

[3256] LINERPT[2:0]

[3257] Each bit, when set, causes the lines of the correspondingcomponent to be read twice (bit 0 affects component 0 etc.). This formsthe first part of the vertical unsampling. It is used in the 8 timeschroma upsampling required for conversion from QFIF to 601.

[3258] COMPOHOLD

[3259] This bit is used to program the ratio of the number of lines tobe read (as opposed to displayed) for component 0 to those of components1 and 2).

[3260] 0: Same number of lines, i.e., 4:4:4 data in the buffers.

[3261] 1: Twice as many component 0 lines, i.e., 4:2:0.

[3262] Page/Block Address Generators (dramctls)

[3263] When passed a line address, these blocks generate a series ofpage/line addresses and blocks to read along the line. The minimum pagewidth of 8 blocks is always assumed and the resulting outputs consist ofa page address, a 3 bit line number, a 3 bit block start, and a 3 bitblock stop address. (The line number is calculated by dline and a passedthrough the dramctls unmodified). Thus, to read out 48 pixels of line 5form page Oxaa starting from the third block from the left (an arbitrarypoint along an arbitrary line), the addresses passed to the DRAMinterface would be:

[3264] Page=Oxaa

[3265] Line=5

[3266] Block start=2

[3267] Block stop=7

[3268] Each of these three machines has 5 datapath registers. These areshown in Table C.3.4. The basic behavior of each dramctl is: Block start= 2 Block stop = 7 Each of these three machines has 5 datapathregisters. These are shown in Table C.3.4 The basic behaviour of eachdramctl is:- while (true) { CNT_LEFT = 0; GET_A_NEW_LINE_ADDRESS fromdline; BLOCK_ADDR = input_block_addr + 0: PAGE_ADDR = input_page_addr +0: CNT_LEFT = DlSP_HBS + 0; while (CNT_LEFT > BLOCKS_LEFT) { BLOCKS_LEFT= 8 − BLOCK_ADDR; → output PAGE_ADDR, start =BLOCK_ADDR, stop =7.PAGE_ADDR = PAGE_ADDR + 1; BLOCK_ADDR = 0; CNT_LEFT = CNT_LEFT −BLOCKS_LEFT; } /* Last Page of line */ CNT_LEFT = CNT_LEFT + BLOCK_ADDR;CNT_LEFT = CNT_LEFT − 1; → outputPAGE_ADDR,start=BLOCK_ADDR,stop=CNT_LEFT }

[3269] TABLE C.3.5 Dramctl (0,1 & 2) Datapath Registers Register NamesBus Keyhole Address Description Comments DISP_COMP0_HBS A 0x48,49,4a,4bThe number of This register DISP_COMP1_HBS A 0x4c,4d,4e,4f horizontalmust be loaded DISP_COMP2_HBS A 0x50,51,52,53 blocks to be before read.c.f. operation can ADDR_HBS begin. CNT_LEFT0 A 0x54,55,56,57 Number ofThese registers CNT_LEFT1 A 0x58,59,5a,5b blocks remaining are temporaryCNT_LEFT2 A 0x5c,5d,5e,5f to be read locations used PAGE_ADDR0 A0x60,61,62,63 The address of by dispaddr PAGE_ADDR1 A 0x64,65,66,67 thecurrent Note: All PAGE_ADDR2 A 0x68,69,6a,6b page. registers are R/BLOCK_ADDR0 B 0x6c,6d,6e,6f Current block W from the upi BLOCK_ADDR1 B0x70,71,72,73 address BLOCK_ADDR2 B 0x74,75,76,77 BLOCKS_LEFT0 B0x78,79,7a,7b Blocks left in BLOCKS_LEFT1 B 0x7c,7d,7e,7f current pageBLOCKS_LEFT2 B 0x80,81,82,83

[3270] Programming

[3271] The following 15 dispaddr registers must be programmed beforeoperation can begin.

[3272] BUFFER_BASE0,1,2

[3273] DISP_COMP_OFFSET0,1,2

[3274] DISP_VBS_COMP0,1,2

[3275] ADDR_HBS_COMP0,1,2

[3276] DISP_COMP0,1,2_HBS

[3277] Using the reset state of the dispaddr control registers will givea 4:2n interlaced display with no line repeats synchronized and startingon the top field (field_info=HIGH). FIG. 159, “Buffer 0 Containing a SIF(22 by 18 macroblocks) picture,” shows a typical buffer setup for a SIFpicture. (This example is covered in more detail in Section C.13). Notethat in this example, DISP_HBS_COMPn is equal to ADDR_HBS_COMPn andlikewise the vertical registers DISPVBSCOMPn and the equivalent writeaddress generator register are equal, i.e., the area to be read is theentire buffer.

[3278] Windowing with the Read Address Generator

[3279] It is possible to program dispaddr such that it will read only aportion (window) of the buffer. The size of the window is programmed foreach component by the registers DISP_HBS, DISP_VBS, COMPONENT_OFFSET,and LINES_INLAST ROW. FIG. 160, “SIF Component 0 with a display window,”shows how this is achieved (for component O only).

[3280] In this example, the register setting would be:

[3281] BUFFER_BASEO O×OO

[3282] DISP_COMP_OFFSETO=O×2D

[3283] DISP_VBS_COMPO=O×22

[3284] ADDR_HBS_COMPO=O×2C

[3285] DISP_HBS_COMO=O×2A

[3286] Notes:

[3287] The window may only start and stop on block boundaries. In thisexample we have left LINES_IN_LAST_ROW equal to 7 (meaning all eight).

[3288] This example is not practical with anything other than 4:4:4data. In order to correspond, the window edges for the other twocomponents could not be on block boundaries.

[3289] The color space converter will hang up if the data it receives isnot 4:4:4. This means that these read windows, in conjunction with theupsamplers must be programmed to achieve this.

[3290] SECTION C.5 Datapaths for Address Generation

[3291] The datapaths used in dispaddr and waddrgen are identical instructure and width (18 bits), only differing in the number ofregisters, some masking, and the flags returned to the state machine.The circuit of one slice is shown in FIG. 165, “Slice Of Datapath,”.Registers are uniquely assigned to drive the A or B bus and their use(assignment) is optimized in the controller. All registers are loadablefrom the C bus, however, not all “load” signals are driven. Alloperations involving the adder cover two cycles allowing the adder tohave ordinary ripple carry. FIG. 166, “Two cycle operation of thedatapath,” shows the timing for the two cycle sum of two registers beingloaded back into the “A” bus register. The various flags are “phO” nedwithin the datapath to allow ccode generation. For the same reason, thestructure of the datapath schematics is a little unusual. The tristatesfor all the registers (onto the A and B buses) are in a single blockwhich eliminates the combinatorial path in the cell, therefore, allowingbetter ccode generation. To gain upi access to the datapaths, the accessbit must be set, for without this, the upi is locked out. Upi access isdifferent from read and write:

[3292] Writing: When the access bit is set, all load signals aredisabled and one of a set of three byte addressed write strobes drivento the appropriate byte of one of the registers. The upi data bus passesvertically down the datapath (replicated, 2-8-8 bits) and the 18 bitregister is written as three separate byte writes

[3293] Reading: This is achieved using the A and B buses. Once again,the access bit must be set. The addressed register is driven onto the Aor B bus and a upi byte select picks a byte from the relevant bus anddrives it onto the upi bus.

[3294] As double cycle datapath operations require the A and B buses toretain their values, and upi accesses disrupt these, access must only begiven by the controlling state machine before the start of any datapathoperation.

[3295] All datapath registers in both address generators are addressedthrough a 9 bit wide keyhole at the top level address O×28 (msb) andO×29 (lsb) for the keyhole, and O×2A for the data. The keyhole addressesare given in Table C.11.2.

[3296] Notes:

[3297] 1)All address registers in the address generators (dispaddr andwaddrgen) contain blocked addresses. Pixel addresses are never used andthe only registers containing line addresses are the threeLINES_IN_LAST_ROW registers.

[3298] 2)Some registers are duplicated between the address generators,e.g., BUFFER BASEO occurs in the address space for dispaddr andwaddrgen. These are two separate registers which BOTH need loading. Thisallows display windowing (only reading a portion of the display store),and eases the display of formats other than 3 component video.

[3299] SECTION C.6 The DRAM Interface

[3300] C.6.1 Overview

[3301] In the present invention, the Spacial Decoder, Temporal Decoderand Video Formatter each contain a DRAM Interface block for thatparticular chip. In all three devices, the function of the DRAMInterface is to transfer data from the chip to the external DRAM andfrom the external DRAM into the chip via block addresses supplied by anaddress generator.

[3302] The DRAM Interface typically operates from a clock which isasynchronous to both the address generator and to the clocks of thevarious blocks through which data is passed. This asynchronism isreadily managed, however, because the clocks are operating atapproximately the same frequency.

[3303] Data is usually transferred between the DRAM Interface and therest of the chip in blocks of 64 bytes (the only exception beingprediction data in the Temporal Decoder). Transfers take place by meansof a device known as a “swing buffer”. This is essentially a pair ofRAMs operated in a double-buffered configuration, with the DRAMinterface filling or emptying one RAM while another part of the chipempties or fills the other RAM. A separate bus which carries an addressfrom an address generator is associated with each swing buffer.

[3304] Each of the chips has four swing buffers, but the function ofthese swing buffers is different in each case. In the Spacial Decoder,one swing buffer is used to transfer coded data to the DRAM, another toread coded data from the DRAM, the third to transfer tokenized data tothe DRAM and the fourth to read tokenized data from the DRAM. In theTemporal Decoder, one swing buffer is used to write Intra or Predictedpicture data to the DRAM, the second to read Intra or Predicted datafrom the DRAM and the other two to read forward and backward predictiondata. In the Video Formatter, one swing buffer is used to transfer datato the DRAM and the other three are used to read data from the DRAM, onefor each of Luminance (Y) and the Red and Blue color difference data (Crand Cb, respectively).

[3305] The operation of a generic DRAM Interface is described in theSpacial Decoder document. The following section describes those featuresof the DRAM Interface, in accordance with the present invention,peculiar to the Video Formatter.

[3306] C.6.2 The Video Formatter DRAM Interface

[3307] In the video formatter, data is written into the external DRAM inblocks, but read out in raster order. Writing is exactly the same asalready described for the Spacial Decoder, but reading is a little morecomplex.

[3308] The data in the Video Formatter external DRAM is organized sothat at least 8 blocks of data fit into a single page. These 8 blocksare 8 consecutive horizontal blocks. When rasterizing, 8 bytes need tobe read out of each of 8 consecutive blocks and written into the swingbuffer (i.e., the same row in each of the 8 blocks).

[3309] Considering the top row (and assuming a byte-wide interface), thex address (the three LSBs) is set to zero, as is the y address (3 MSBs).The x address is then incremented as each of the first 8 bytes are readout. At this point, the top part of the address (bit 6 and above—LSB=bit0) is incremented and the x address (3 LSBs) is reset to zero. Thisprocess is repeated until 64 bytes have been read. With a 16 or 32 bitwide interface to the external DRAM, the x address is merely incrementedby two or four instead of by one.

[3310] The address generator can signal to the DRAM Interface that lessthan 64 bytes should be read (this may be required at the beginning orend of a raster line) although a multiple of 8 bytes is always read.This is achieved by using start and stop values. The start value is usedfor the top part of the address (bit 6 and above), and the stop value iscompared with this and a signal generated which indicates when readingshould stop.

[3311] SECTION C.7 Vertical Upsampling

[3312] C.7.1 Introduction

[3313] Given a raster scan of pixels of one color component at itsinput, the vertical upsampler in accordance with the present invention,can provide an output scan of twice the height. Mode selection allowsthe output pixel values to be formed in a number of ways.

[3314] C.7.2 Ports

[3315] Input two wire interface:

[3316] invalid

[3317] inaccept

[3318] indata[7:0]

[3319] in lastpel

[3320] in lastline

[3321] Output two wire interface:

[3322] outvalid

[3323] out accept

[3324] out data[9:0]

[3325] outlast

[3326] mode[2:0]

[3327] nupdata[7:0], upaddr, upsel[3:0], uprstr, upwstr ramtest

[3328] tdin, tdout, tpho, tckm, tcks

[3329] phO, phl, notrstO

[3330] C.7.3 Mode

[3331] As selected by the input bus mode∂2:0].

[3332] Mode register values 1 and 7 are not used.

[3333] In each of the above modes, the output pixels are represented aslo-bit values, not as bytes. No rounding or truncation takes place inthis block. Where necessary, values are shifted left to use the samerange.

[3334] C.7.3.1 Mode O:Fifo

[3335] The block simply acts as a FIFO store. The number of outputpixels is exactly the same as at the input. The values are shifted leftby two.

[3336] C.7.3.2 Mode 2: Repeat

[3337] Every line in the input scan is repeated to produce an outputscan twice as high. Again, the pixel values are shifted left by two.

[3338] A->ABACBDBCCDD

[3339] C.7.3.3 Mode 4: Lower

[3340] Each input line produces two output lines. In this “lower” mode,the second of these two lines (the lower on the display) is the same asthe input line. The first of the pair is the average of the currentinput line and the previous input line. In the case of the first inputline, where there is no previous line to use, the input line isrepeated.

[3341] This should be selected where chroma samples are co-sited withthe lower luma samples.

[3342] A→ABAC(A+B)/2DB(B+C)/2C(C+D)/2D

[3343] C.7.3.4 Mode 5: Upper

[3344] Similar to the “lower” mode, but in this case the input lineforms the upper of the output pair, and the lower is the average ofadjacent input lines. The last output line is a repeat of the last inputline.

[3345] This should be selected where chroma samples are co-sited withthe upper luma samples.

[3346] A->AB(A+B)/2CBD(B+C)/2C(C+D)/2DD

[3347] C.7.3.5 Mode 6: Central

[3348] This “central” mode corresponds to the situation where chromasamples lie midway between luma samples. In order to co-site the outputchroma pixels with the luma pixels, a weighted average is used to formthe output lines.

[3349] A->AB(3A+B)/4C(A+3B)/4D(3B C)/4(B+3C)/4 (3CD)/4(C+3D)/4D

[3350] C.7.4 How it Works

[3351] There are two linestores, imaginatively designated “a” and “b”.In “FIFO” and “repeat” modes, only linestore “a” is used. Each store canaccommodate a line of up to 512 pixels (vertical upsampling should beperformed before any horizontal upsamplng) There is no restriction onthe length of the line in “FIFO” mode.

[3352] The input signals in_last_pel and in lastline are used toindicate the end of the input line and the end of the picture.In_last_pel, it should be high coincident with the last pixel of eachline. In_lastline, it should be high coincident with the last pixel orthe last line of the picture.

[3353] The output signal out_last is high coincident with the last pixelof each output line.

[3354] In “repeat” mode, each line is written into store “al”. The lineis then read out twice. As it is read out for the second time, the nextline may start to be written.

[3355] In “lower”, “upper” and “central” modes, lines are writtenalternately into stores “a” and “b”. The first line of a picture isalways written into store “a”. Two tiny state machines, one for eachstore, keep track of what is in each store and which output line isbeing formed. From these states are generated the read and writerequests to the linestore RAMs, and the signals that determine when thenext line may overwrite the present data.

[3356] A register (lastaddr) stores the write address when in lastpel ishigh, thereby providing the length of the line for the formation of theoutput lines.

[3357] C.7.5 UPI

[3358] This block contains two 512×8 bit RAM arrays, which may beaccessed via the microprocessor interface in the typical way. There areno registers with microprocessor access.

[3359] SECTION C.8 The Horizontal Up-samplers

[3360] C.8.1 Overview

[3361] In the present invention, top-Level Registers contain threeidentical Horizontal Up-samplers, one for each color component. Allthree are controlled independently and, therefore, only one need bedescribed here. From the user's point of view, the only difference isthat each Horizontal Up-sampler is mapped into a different set ofaddresses in the memory map.

[3362] The Horizontal Up-sampler performs a combined replication andfiltering operation. In all, there are four modes of operation: TABLEC.7.1 Horizontal Up-sampler Modes Mode Function 0 Straight-through (noprocessing). The reset state. 1 No up-sampling, filter using a 3-tap FIRfilter. 2 x2 up-sampling and filtering 3 x4 up-sampling and filtering

[3363] C.8.2 Using a Horizontal Up-sampler

[3364] The address map for each Horizontal Up-sampler consists of 25locations corresponding to 12 13-bit coefficient registers and one 2-bitmode register. The number written to the mode register determines themode of operation, as outlined in Table C.7.1. Depending on the mode,some or all of the coefficient registers may be used. The equivalent FIRfilter is illustrated below. Depending on the mode of operation, theinput, x_(n), is held constant for one, two or four clock periods. Theactual coefficients that are programmed for each mode are as follows:TABLE C.7.2 Coefficients for Mode 1 Coeff All clock periods k0 c00 k1c10 k2 c20

[3365] TABLE C.7.3 Coefficients for Mode 2 Coeff 1st clock period 2ndclock period k0 c00 c01 k1 c10 c11 k2 c20 c21

[3366] TABLE C.7.4 Coefficients for Mode 3 1st clock 2nd clock 3rd clock4th clock Coeff period period period period k0 c00 c01 c02 c03 k1 c10c11 c12 c13 k2 c20 c21 c22 c23

[3367] Coefficients which are not used in a particular mode need not beprogrammed when operating in that mode.

[3368] In order to achieve symmetrical filtering, the first and lastpixels of each line are repeated prior to filtering.

[3369] For example, when up-sampling by two, the first and last pixelsof each line are replicated four times rather than two. Because residualdata in the filter is discarded at the end of each line, the number ofpixels output is still always exactly one, two or four times the numberin the input stream.

[3370] Depending on the values of the coefficients, output samples canbe placed either coincident with or shifted from the input samples.Following are some example values for coefficients in some sample modes.A “-” indicates that the value of the coefficient is “don't care.” Allvalues are in hexadecimal. TABLE C.7.5 Sample Coefficients x2 up-sample,x2 up-sample, x4 up-sample, o/p pels o/p pels in o/p pels in Coefficientcoincident with i/p between i/p between i/p c00 0000 01BD 00E9 c01 0000010B 00B6 c02 — — 012A c03 — — 0102 c10 0800 0538 0661 c11 0400 05380661 c12 — — 0446 c13 — — 029F c20 0000 010B 00B6 c21 0400 01BD 00E9 c22— — 0290 c23 — — 045F

[3371] C.b 8.3 Description of a Horizontal Up-sampler

[3372] The datapath of the Horizontal Up-sampler is illustrated in FIG.168.

[3373] The operation is outlined below for the x4 upsample case. Inaddition, x2 upsampling and x1 filtering (modes 2 and 1) are degeneratecases of this, and bypass (mode 0) the entire filter, data passingstraight from the input latch to the output latch via the final mux, asillustrated.

[3374] 1)When valid data is latched in the input latch (“L”), it is heldfor 4 clock periods.

[3375] 2)The coefficient registers (labelled “COEFF”) are multiplexedonto the multipliers for one clock period, each in turn, at the sametime as the two sets of four pipeline registers (labelled “PIPE”) areclocked. Thus, for input data x₀, the first PIPE will fill up with thevalues cOO.x₀, cO1.x₀, cO2.x₀, cO3.x₀.

[3376] 3)Similarly, the second multiplier will multiply 4 by of itscoefficients, in turn, and the third multiplier by all its coefficients,in turn.

[3377] It can be seen that the output will be of the form shown in TableC.7.6 TABLE C.7.6 Output Sequence for Mode 3 ClockI Penod Ouput 0c20.x_(n) + c10.x_(n−1) + c00.x_(n−2) 1 c21.x_(n) + c11.x_(n−1) +c01.x_(n−2) 2 c22.x_(n) + c12.x_(n−1) + c02.x_(n−2) 3 c23.x_(n) +c13.x_(n−1) + c03.x_(n−2)

[3378] From the point of view of the output, each clock period producesan individual pixel. Since each output pixel is dependent on theweighted values of 12 input pixels (although there are only threedifferent values), this can be thought of as implementing a 12 tapfilter on x4 up-sampled input pixels.

[3379] For x2 upsampling, the operation is essentially the same, exceptthe input data is only held for two clock periods. Furthermore, only twocoefficients are used and the “PIPE” blocks are shortened by means ofthe multiplexers illustrated. For x1 filtering, the input is only heldfor one clock period. As expected, one coefficient and one “PIPE” stageare used.

[3380] We now discuss a few notes about some peculiarities of theimplementation in the present invention.

[3381] 1)The datapath width and coefficient width (13 bit 2'scomplement) were chosen so that the same multiplier could be used, aswas designed for the Color-Space Converter. These widths are more thanadequate for the purpose of the Horizontal Up-sampler.

[3382] 2)The multiplexers which multiplex the coefficients onto themultipliers are shared with the UPI readback. This has led to somecomplications in the structure of the schematics (primarily because ofdifficulty in CCODE generation), but the actual circuit is smaller.

[3383] 3)As in the Color-Space Converter, carry-save multipliers areused, the result only being resolved at the end.

[3384] Control for the entire Horizontal Up-sampler can be regarded as asingle two-wire interface stage which may produce two or four times theamount of data at its output as there is on its input. The mode which isprogrammed in via the UPI determines the length of a programmable shiftregister (bob). The selected mode produces an output pulse every clockperiod, every two clock periods or every four clock periods. This, inturn, controls the main state machine, whose state is also determined byin_valid, out_accept (for the two-wire interface) and the signal“in_last”. This signal is passed on from the vertical up-sampler and ishigh for the last pixel of every line. This allows the first and lastpixels of each line to be replicated twice-over and the clearing down ofthe pipeline between lines (the pipeline contains partially-processedredundant data immediately after a line has been completed).

[3385] SECTION C.9 The Color-Space Converter

[3386] C.9.1 Overview

[3387] The Color-Space Converter in the present invention (CSC) performsa 3×3 matrix multiplication on the incoming 9-bit data, followed by anaddition: $\begin{bmatrix}{y0} \\{y1} \\{y2}\end{bmatrix} = {{\begin{bmatrix}{c01} & {c02} & {c03} \\{c11} & {c12} & {c13} \\{c12} & {c22} & {c23}\end{bmatrix} \times \begin{bmatrix}{x0} \\{x1} \\{x2}\end{bmatrix}} + \begin{bmatrix}{c04} \\{c14} \\{c24}\end{bmatrix}}$

[3388] Where xO-2 are the input data, yO-2 are the output data and cnmare the coefficients. The slightly unconventional naming of the matrixcoefficients is deliberate, since the names correspond to signal namesin the schematics.

[3389] The CSC is capable of performinq conversions between a number ofdifferent color spaces although a limited set of these conversions areused in Top-Level Registers. The design color-space conversions are asfollows: $\begin{matrix}{E_{R},E_{G}, E_{B}arrow Y ,C_{R},C_{B}} \\{R,G, Barrow Y ,C_{R},C_{B}} \\{Y,C_{R}, C_{B}arrow E_{R} ,E_{G},E_{B}} \\{Y,C_{R}, C_{B}arrow R ,G,B}\end{matrix}$

[3390] Where R, G and B are in the range (0.511) and all otherquantities are in the range of (32.470). Since the input to theTop-Level Registers CSC is Y, C_(R), C_(B), only the third and fourth ofthese equations are of relevance.

[3391] In the CSC design, the precision of the coefficients was chosenso that, for 9 bit data, all output values were within plus or minus 1bit of the values produced by a full floating point simulation of thealgorithm (this is the best accuracy that it is possible to achieve).This gave 13 bit twos-complement coefficients for cxO-cx3 and 14 bittwos-complement coefficients for cx4. The coefficients for all thedesign conversions are given below in both decimal and hex. TABLE C.8.1Coefficients for Various Conversions Eq−>Y R−>Y Y−>Eq Y−>R Coeff Dec HexDec Hex Dec Hex Dec Hex c01  0.299 0132 0.256 1.0 0400 1.159 C44D c02 0.587 0259 0.502 1.402 059C 1.539 C88E c03  0.114 0075 0.098 0.0 00000.0 0000 c04  0.0 0000 16 −179.456 F4C8 −228.478 F153 c11 0.5 0200 0.4281.0 0400 1.159 D4AC c12 −0.419 FE53 −0.358 −0.714 FD25 −0.335 FCA9 C13−0.081 FFAD −0.070 −0.344 FEA0 −0.402 FE54 c14 128.0 0800 128 135.5 0878139.7 CEBA c21 −0.169 FF53 −0.144 1.0 0400 1.159 C4AD c22 −0.331 FEAD−0.283 0.0 0000 0.0 C880 c23 0.5 0200 0.427 1.772 0717 2.071 C849 c24128 0800 128 −226.816 F1D2 −283.84 EE42

[3392] All these numbers are calculated from the fundamental equation:

Y=0.299E _(R)+0.587E _(G)+0.0114E _(B)

[3393] and the following color-difference equations:

C _(R) =E _(R) −Y

C _(B) =E _(B) −Y

[3394] The equations in R, G and B are derived from these after thefull-scale ranges of these quantities are considered,

[3395] C.9.2 Using the Color-space Converter

[3396] On reset, cO1, c12, and c23 are set to 1 and all othercoefficients are set to 0. Thus, y0=x0, y1=x1 and y2=x2 and all data ispassed through unaltered. To select a color-space conversion, simplywrite the appropriate coefficients (from Table C.8.1, for example) intothe locations specified in the address map.

[3397] Referring to the schematics, x0..2 correspond to in data0..2 andy0..2 correspond to out_data0..2. Users should remember that input datato the CSC must be up-sampled to 4:4:4. If this is not the case, notonly will the color-space transforms have no meaning, but the chip willlock.

[3398] It should be noted that each output can be formed from anyallowed combination of coefficients and inputs plus (or minus) aconstant. Thus, for any given color-space conversion, the order of theoutputs can be changed by swapping the rows in the transform matrix(i.e., the addresses into which the coefficients are written).

[3399] The CSC is guaranteed to work for all the transforms in TableC.8.1. If other transforms are used the user must remember thefollowing:

[3400] 1)The hardware will not work if any intermediate result in thecalculation requires greater than 10 bits of precision (excluding thesign bit).

[3401] 2)The output of the CSC is saturated to 0 and 511. That is, anynumber less than 0 is replaced with 0 and any number more than 511 isreplaced with 511. The implementation of the saturation logic assumesthat the results will only be slightly above 511 or slightly below 0. Ifthe CSC is programmed incorrectly, then a common symptom will be thatthe output appears to saturate all (or most of) the time.

[3402] C.9.3 Description of the C8C

[3403] The structure of the CSC is illustrated in FIG. 169, where onlytwo of the three “components” have been shown because of spacelimitations. In the Figure, “register” or “R” implies a master-slaveregister and “latch” or “L” implies a transparent latch.

[3404] All coefficients are loaded into read-write UPI registers whichare not shown explicitly in the Figure. To understand the operation,consider the following sequence with reference to the left-most“component” (that which produces output out_data0):

[3405] 1)Data arrives at inputs x0-2 (in_data0-2). This represents asingle pixel in the input color-space. This is latched.

[3406] 2)x0 is multiplied by c01 and latched into the first pipelineregister. x1 and x2 move on one register.

[3407] 3)x1 is multiplied by c02, added to (x1.c01) and latched into thenext pipeline register. x2 moves on one register.

[3408] 4)x2 is multiplied by c03 and added to the result of (3),producing (x1.c01+x2.c02+x3.c03). The result is latched into the nextpipeline register.

[3409] 5)The result of (4) is added to c04. Since data is kept incarry-save format through the multipliers, this adder is also used toresolve the data from the multiplier chain. The result is latched in thenext pipeline register.

[3410] 6)The final operation is to saturate the data. Partial resultsare passed from the resolving adder to the saturate block to achievethis.

[3411] It can be seen that the result is y0, as specified in the matrixequation at the start of this section. Similarly, y1 and y2 are formedin the same manner.

[3412] Three multipliers are used, with the coefficients as themultiplicand and the data as the multiplicator. This allows an efficientlayout to be achieved, with partial results flowing down the datapathand the same input data being routed across three parallel and identicaldatapaths, one for each output.

[3413] To achieve the reset state described in Section C.9.2, each ofthe three “components” must be reset in a different way. In order toavoid having three sets of schematics and three slightly differentlayouts, this is achieved by having inputs to the UPI registers whichare tied high or low at the top level.

[3414] The CSC has almost no control associated with it. Nevertheless,each pipeline stage is a two-wire interface stage, so there is a chainof valid and accept latches with their associated control(in_accept=out_accept_r+lin_valid_r). The CSC is, therefore, a 5-stagedeep two-wire interface, capable of holding 10 levels of data whenstalled.

[3415] The output of the CSC contain re-synchronizing latches becausethe next function in the output pipe runs off a different clockgenerator.

[3416] SECTION C.10 Output Controller

[3417] C10.1 Introduction

[3418] The output controller, in accordance with the present invention,handles the following functions:

[3419] It provides data in one of three modes

[3420] 24-bit 4:4:4

[3421] 16-bit 4:2:2

[3422] 8-bit 4:2:2

[3423] It aligns the data to the video display window defined 90 by thevsync and hsync pulses and by programmed timing registers

[3424] It adds a border around the video window, if required

[3425] C.10.2 Ports

[3426] Input two wire interface:

[3427] in valid

[3428] in_accept

[3429] in_data[23:0]

[3430] Output two wire interface:

[3431] out_valid

[3432] out_accept

[3433] out_data[23:0]

[3434] out_active

[3435] out_window

[3436] out_comp[1:0]

[3437] in_vsync, in_hsync

[3438] nupdata[7:0], upaddr[4:0], upsel, rstr, wstr

[3439] tdin, tdout, tpho, tckm, tcks chiptest phO, phl, notrstO, notrstl

[3440] C.10.3 Out Modes

[3441] The format of the output is selected by writing to the opmoderegister.

[3442] C10.3.1 Mode O

[3443] This mode is 24-bit 4:4:4 RGB or YCrCb. Input data passesdirectly to the output.

[3444] C.10.3.2 Modes 1 and 2

[3445] These modes present 4:2:2 YCrCb. Assuming in_data[23:16] is Y,in_data[15:8] is Cr and in_data[7:0] is Cb.

[3446] C.10.3.2.1 Mode 1

[3447] In 16-bit YCrCb, Y is presented on out_data[15:8]. Cr and Cb aretime multiplexed on out_data[7:0], Cb first. Out_data[23:16] is notused.

[3448] C.10.3.2.2 Mode 2

[3449] In 8-bit YCrCb, Y,Cr and Cb are time multiplexed on out_data[7:0]in the order Cb, Y, Cr, Y. Out_data[23:8] is not used.

[3450] C.10.3.3 Output Timing

[3451] The following registers are used to place the data in a videodisplay window.

[3452] vdelay—The number of hsync pulses following a vsync pulse beforethe first line of video or border.

[3453] hdelay—The number of clock cycles between hsync and the firstpixel of video or border.

[3454] height—The height of the video window, in lines.

[3455] width—The width of the video window, in pixels.

[3456] north, south—The height of the border, respectively, above andbelow the video window, in lines.

[3457] west, east—The width of the border, respectively, to the left andto the right of the video window, in pels.

[3458] The minimum vdelay is zero. The first hsync is the first activeline. The minimum value that can be programmed into hdelay is 2. Note,however, that the actual delay from in_hsync to the first active outputpixel is hdelay+1 cycles.

[3459] Any edge of the border can have the value zero. The color of theborder is selected by writing to the registers border_r, border_g andborder_b. The color of the area outside the border is selected bywriting to the registers blank_r, blank_g and blank_b. Note that themultiplexing performed in output modes 1 and 2 will also affect theborder and blank.components. That is, the values in these registerscorrespond with in_data[23:16], in_data[15:8] and in_data[7:0].

[3460] C.10.4 Output Flags

[3461] out_active indicates that the output data is part of the activewindow, i.e., video data or border.

[3462] out_window indicates that the output data is part of the videowindow.

[3463] out_comp[1:0] indicates which color component is present onout_data[7:0] in output modes 1 and 2. In mode 1, 0=Cb, 1=Cr. In mode 2,0=Y, 1=Cr, 2=Cb.

[3464] C.10.5 Two-wire Mode

[3465] The two-wire mode of the present invention is selected by writing1 to the two wire register. It is not selected following reset. In twowire mode, the output timing registers and sync signals are ignored andthe flow of data through the block is controlled by out_accept. Notethat in normal operation, out_accept should be tied high.

[3466] C.10.6 Snooper

[3467] There is a super-snooper on the output of the block whichincludes access to the output flags.

[3468] C.10.7 Now it Works

[3469] Two identical down-counters keep track of the current position inthe display. “Vcount” decrements on hsyncs and loads from theappropriate timing register on vsync or at its terminal count. “Hcount”decrements on every pixel and loads on hsync or at its terminal count.Note that in output mode 2, one pixel corresponds to two clock cycles.

[3470] SECTION C.11 The Clock Dividers

[3471] C.11.1 Overview

[3472] Top-Level Registers in the present invention contain twoidentical Clock Dividers, one to generate a PICTURE_CLK and one togenerate an AUDIO_CLK. The Clock Dividers are identical and arecontrolled independently. Therefore, only one need be described here.From the user's point of view, the only difference is that each ClockDivider's divisor register is mapped into a different set of addressesin the memory map.

[3473] The Clock Divider's function is to provide a 4X sysclk dividedclock frequency, with no requirement for an even mark-space ratio.

[3474] The divisor is required to lay in the range −0 to −16,000,000and, therefore, it can be represented using 24bits with the restrictionthat the minimum divisor be 16. This is because the Clock Divider willapproximate an equal mark-space ratio (to within one sysclk cycle) byusing divisor/2. As the maximum clock frequency available is sysclk, themaximum divided frequency available is sysclk/2. Furthermore, becausefour counters are used in cascade divisor/2 must never be less than 8,else the divided clock output will be driven to the positive power rail.

[3475] C.11.2 Using a Clock Divider

[3476] The address map for each Clock Divider consists of 4 locationscorresponding to three 8-bit divisor registers and one 1-bit accessregister. The Clock Divider will power-up inactive and is activated bythe completion of an access to its divisor register.

[3477] The divisor registers may be written in any order according tothe address map in Table C.10.1. The Clock Divider is activated bysensing a synchronized 0 to 1 transition in its access bit. The firsttime a transition is sensed, the Clock Divider will come out of resetand generate a divided clock. Subsequent transitions (assuming thedivisor has also been altered) will merely cause the Clock Divider tolock to its new frequency “on-the-fly.” Once activated, there is no wayof halting the Clock Divider other than by Chip RESET. TABLE C.10.1Clock Divider Registers Address Register 00b access bit 01b divisor MSB10b divisor 11b divisor LSB

[3478] Any divisor value in the range 16 to 16,777,216 may be used.

[3479] C.11.3 Description of the Clock Divider

[3480] The Clock Divider is implemented as four 22 bit counters whichare cascaded such that as one counter carries, it will activate the nextcounter in turn. A counter will count down the value of divisor/4 beforecarrying and, therefore, each counter will take it, in turn, to generatea pulse of the divided clock frequency.

[3481] After carrying, the counter will reload with divisor/8 and thisis counted down to produce the approximate equal mark-space ratiodivided clock. As each counter reloads from the divisor register when itis activated by the previous counter, this enables the divided clockfrequency to be changed on the fly by simply altering the contents ofthe divisor.

[3482] Each counter is clocked by its own independent clock generator inorder to control clock skew between counters precisely and to allow eachcounter to be clocked by a different set of clocks.

[3483] A state machine controls the generation of the divisor/4 anddivisor/8 values and also multiplexes the correct source clocks from thePLL to the clock generators. The counters are clocked by differentclocks dependent on the value of the divisor. This is because differentdivisor values will produce a divided clock whose edges are placed usingdifferent combinations of the clocks provided from the PLL.

[3484] C.11.4 Testing the Clock Divider

[3485] The Clock Divider may be tested by powering up the Chip withCHIPTEST High. This will have the effect of forcing all of the clockedlogic in the Clock Divider to be clocked by sysclk, as opposed to, theclocks generated by the PLL.

[3486] The Clock Divider has been designed with full scan and, thus, maysubsequently be tested using standard JTAG access, as long as the Chiphas been powered up as above.

[3487] The functionality of the Clock Divider is NOT guaranteed ifCHIPTEST is held High while the device is running in normal operation.

[3488] SECTION C.12 Address Niaps

[3489] C.12.1 Top Level Address Map

[3490] Notes:

[3491] 1)The register for the Top Level Address Map as set forth inTable C.11.1 are the names used during the design. They are notnecessarily the names that will appear-on the datasheet.

[3492] 2)Since this is a full address map, many of the locations listedhere include locations for test only. TABLE C.11.1 Top-Level Registers ATop Level Address Map REGISTER NAME Address Bits COMMENT BU_EVENT 0x0 8Write 1 to reset BU_MASK 0x1 8 R/W BU_EN_INTERRUPTS 0x2 1 R/WBU_WADDR_COD_STD 0x4 2 R/W BU_WADDR_ACCESS 0x5 1 R/W - accessBU_WADDR_CTL1 0x6 3 R/W BU_DISPADDR_LINES_IN_LAST_ROW0 0x8 3 R/WBU_DISPADDR_LINES_IN_LAST_ROW1 0x9 3 R/W BU_DISPADDR_LINES_IN_LAST_ROW20xa 3 R/W BU_DISPADDR_ACCESS 0xb 1 R/W - access BU_DISPADDR_CTL0 0xc 8R/W BU_DISPADDR_CTL1 0xd 1 R/W BU_BM_ACCESS 0x10 1 R/W - accessBU_BM_CTL0 0x11 2 R/W BU_BM_TARGET_IX 0x12 4 R/W BU_BM_PRES_NUM 0x13 8R/W - asynchronous BU_BM_THIS_PNUM 0x14 8 R/W BU_BM_PIC_NUM0 0x15 8 R/WBU_BM_PIC_NUM1 0x16 8 R/W BU_BM_PIC_NUM2 0x17 8 R/W BU_BM_TEMP_REF 0x185 RO BU_ADDRGEN_KEYHOLE_ADDR_MSB 0x28 1 R/W - Address generatorBU_ADDRGEN_KEYHOLE_ADDR_LSB 0x29 8 keyhcle. See BU_ADDRGEN_KEYHOLE_DATA0x2a 8 Table C.11.2 for contents BU_IT_PAGE_START 0x30 5 R/WBU_IT_READ_CYCLE 0x31 4 R/W BU_IT_WRITE_CYCLE 0x32 4 R/WBU_IT_REFRESH_CYCLE 0x33 4 R/W BU_IT_RAS_FALLING 0x34 4 R/WBU_IT_CAS_FALLING 0x35 4 R/W BU_IT_CONFIG 0x36 1 R/W BU_OC_ACCESS 0x40 1R/W - access BU_OC_MODE 0x41 2 R/W BU_OC_2WIRE 0x42 1 R/W BU_OC_BORDER_R0x49 8 R/W BU_OC_BORDER_G 0x4a 8 R/W BU_OC_BORDER_B 0x4b 8 R/WBU_OC_BLANK_R 0x4d 8 R/W BU_OC_BLANK_G 0x4e 8 R/W BU_OC_BLANK_B 0x4f 8R/W BU_OC_HDELAY_1 0x50 3 R/W BU_OC_HDELAY_0 0x51 8 R/W BU_OC_WEST_10x52 3 R/W BU_OC_WEST_0 0x53 8 R/W BU_OC_EAST_1 0x54 3 R/W BU_OC_EAST_00x55 8 R/W BU_OC_WIDTH_1 0x56 3 R/W BU_OC_WIDTH_0 0x57 8 R/WBU_OC_VDELAY_1 0x58 3 R/W BU_OC_VDELAY_0 0x59 8 R/W BU_OC_NORTH_1 0x5a 3R/W BU_OC_NORTH_0 0x5b 8 R/W BU_OC_SOUTH_1 0x5c 3 R/W BU_OC_SOUTH_0 0x5d8 R/W BU_OC_HEIGHT_1 0x5e 3 R/W BU_OC_HEIGHT_0 0x5f 8 R/WBU_IF_CONFIGURE 0x60 5 R/W BU_UV_MODE 0x61 6 R/W - xnnnxnnnBU_COEFF_KEYADDR 0x62 7 R/W - See Table C.11.3 BU_COEFF_KEYDATA 0x63 8for contents. BU_GA_ACCESS 0x68 1 R/W BU_GA_BYPASS 0x69 1 R/WBU_GA_RAM0_ADDR 0x6a 8 R/W BU_GA_RAM0_DATA 0x6b 8 R/W BU_GA_RAM1_ADDR0x6c 8 R/W BU_GA_RAM1_DATA 0x6d 8 R/W BU_GA_RAM2_ADDR 0x6e 8 R/WBU_GA_RAM2_DATA 0x6f 8 R/W BU_DIVA_3 0x70 1 R/W BU_DIVA_2 0x71 8 R/WBU_DIVA_1 0x72 8 R/W BU_DIVA_0 0x73 8 R/W BU_DIVP_3 0x74 1 R/W BU_DIVP_20x75 8 R/W BU_DIVP_1 0x76 8 R/W BU_DIVP_0 0x77 8 R/W BU_PAD_CONFIG_10x78 7 R/W BU_PAD_CONFIG_0 0x79 8 R/W BU_PLL_RESISTORS 0x7a 8 R/WBU_REF_INTERVAL 0x7b 8 R/W BU_REVISION 0xff 8 RO-revision The followingregisters are in the “test space”. They are unlikely to appear on thedatasheet. BU_BM_PRES_FLAG 0x80 1 R/W BU_BM_EXP_TR 0x81 — Theseregisters are BU_BM_TR_DELTA 0x82 — missing on revA BU_BM_ARR_IX 0x83 2R/W BU_BM_DSP_IX 0x84 2 R/W BU_BM_RDY_IX 0x85 2 R/W BU_BM_BSTATE3 0x86 2R/W BU_BM_BSTATE2 0x87 2 R/W BU_BM_BSTATE1 0x88 2 R/W BU_BM_INDEX 0x89 2R/W BU_BM_STATE 0x8a 5 R/W BU_BM_FROMPS 0x8b 1 R/W BU_BM_FROMFL 0x8c 1R/W BU_DA_COMP0_SNP3 0x90 8 R/W - These are the three BU_DA_COMP0_SNP20x91 8 snoopers on the display BU_DA_COMP0_SNP1 0x92 8 addressgenerators BU_DA_COMP0_SNP0 0x93 8 address output BU_DA_COMP1_SNP3 0x948 BU_DA_COMP1_SNP2 0x95 8 BU_DA_COMP1_SNP1 0x96 8 BU_DA_COMP1_SNP0 0x978 BU_DA_COMP2_SNP3 0x98 8 BU_DA_COMP2_SNP2 0x99 8 BU_DA_COMP2_SNP1 0x9a8 BU_DA_COMP2_SNP0 0x9b 8 BU_UV_RAM1A_ADDR_1 0xa0 8 R/W - upi testaccess into BU_UV_RAM1A_ADDR_0 0xa1 8 the vertical upsamplersBU_UV_RAM1A_DATA 0xa2 8 RAMs BU_UV_RAM1B_ADDR_1 0xa4 8BU_UV_RAM1B_ADDR_0 0xa5 8 BU_UV_RAM1B_DATA 0xa6 8 BU_UV_RAM2A_ADDR_10xa8 8 BU_UV_RAM2A_ADDR_0 0xa9 8 BU_UV_RAM2A_DATA 0xaa 8BU_UV_RAM2B_ADDR_1 0xac 8 BU_UV_RAM2B_ADDR_0 0xad 8 BU_UV_RAM2B_DATA0xae 8 BU_WA_ADDR_SNP2 0xb0 8 R/W - snooper on the write BU_WA_ADDR_SNP10xb1 8 address generator address BU_WA_ADDR_SNP0 0xb2 8 o/p.BU_WA_DATA_SNP1 0xb4 8 R/W - snooper on data BU_WA_DATA_SNP0 0xb5 8output of WA BU_IF_SNP0_1 0xb8 8 R/W - Three snoopers on. BU_IF_SNP0_00xb9 8 the dramif data outputs. BU_IF_SNP1_1 0xba 8 BU_IF_SNP1_0 0xbb 8BU_IF_SNP2_1 0xbc 8 BU_IF_SNP2_0 0xbd 8 BU_IFRAM_ADDR_1 0xc0 1 R/W - upiaccess it IF RAM BU_IFRAM_ADDR_0 0xc1 8 BU_IFRAM_DATA 0xc2 8 BU_OC_SNP_30xc4 8 R/W - snooper on output of BU_OC_SNP_2 0xc5 8 chip BU_OC_SNP_10xc6 8 BU_OC_SNP_0 0xc7 8 BU_YAPLL_CONFIG 0xc8 8 R/W BU_BM_FRONT_BYPASS0xca 1 R/W

[3493] C.12.1 Address Generator Keyhole Space

[3494] Notes an address generator keyhole table:

[3495] 1)All registers in the address generator keyhole take up 4 bytesof address space regardless of their width. The missing addresses (0×00,0×04 etc.) will always read back zero.

[3496] 2)The access bit of the relevant block (dispaddr or waddrgen)must be set before accessing this keyhole. TABLE C.11.2 Top-LevelRegistersA Address Generator Keyhole Keyhole Keyhole Register NameAddress Bits Comments BU_DISPADDR_BUFFER0_BASE_MSB 0x01 2 18 bitBU_DISPADDR_BUFFER0_BASE_MID 0x02 8 registerBU_DISPADDR_BUFFER0_BASE_LSB 0x03 8 Must be LoadedBU_DISPADDR_BUFFER1_BASE_MSB 0x05 2 Must be BU_DISPADDR_BUFFER1_BASE_MID0x06 8 Loaded BU_DISPADDR_BUFFER1_BASE_LSB 0x07 8BU_DISPADDR_BUFFER2_BASE_MSB 0x09 2 Must be BU_DISPADDR_BUFFER2_BASE_MID0x0a 8 Loaded BU_DISPADDR_BUFFER2_BASE_LSB 0x0b 8 BU_DLDPATH_LINE0_MSB0x0d 2 Test only BU_DLDPATH_LINE0_MID 0x0e 8 BU_DLDPATH_LINE0_LSB 0x0f 8BU_DLDPATH_LINE1_MSB 0x11 2 Test only BU_DLDPATH_LINE1_MID 0x12 8BU_DLDPATH_LINE1_LSB 0x13 8 BU_DLDPATH_LINE2_MSB 0x15 2 Test onlyBU_DLDPATH_LINE2_MID 0x16 8 BU_DLDPATH_LINE2_LSB 0x17 8BU_DLDPATH_VBCNT0_MSB 0x19 2 Test only BU_DLDPATH_VBCNT0_MID 0x1a 8BU_DLDPATH_VBCNT0_LSB 0x1b 8 BU_DLDPATH_VBCNT1_MSB 0x1d 2 Test onlyBU_DLDPATH_VBCNT1_MID 0x1e 8 BU_DLDPATH_VBCNT1_LSB 0x1f 8BU_DLDPATH_VBCNT2_MSB 0x21 2 Test only BU_DLDPATH_VBCNT2_MID 0x22 8BU_DLDPATH_VBCNT2_LSB 0x23 8 BU_DISPADDR_COMP0_OFFSET_MSB 0x25 2 Must beBU_DISPADDR_COMP0_OFFSET_MID 0x26 8 Loaded BU_DISPADDR_COMP0_OFFSET_LSB0x27 8 BU_DISPADDR_COMP1_OFFSET_MSB 0x29 2 Must beBU_DISPADDR_COMP1_OFFSET_MID 0x2a 8 Loaded BU_DISPADDR_COMP1_OFFSET_LSB0x2b 8 BU_DISPADDR_COMP2_OFFSET_MSB 0x2d 2 Must beBU_DISPADDR_COMP2_OFFSET_MID 0x2e 8 Loaded BU_DISPADDR_COMP2_OFFSET_LSB0x2f 8 BU_DISPADDR_COMP0_VBS_MSB 0x31 2 Must beBU_DISPADDR_COMP0_VBS_MID 0x32 8 Loaded BU_DISPADDR_COMP0_VBS_LSB 0x33 8BU_DISPADDR_COMP1_VBS_MSB 0x35 2 Must be BU_DISPADDR_COMP1_VBS_MID 0x368 Loaded BU_DISPADDR_COMP1_VBS_LSB 0x37 8 BU_DISPADDR_COMP2_VBS_MSB 0x392 Must be BU_DISPADDR_COMP2_VBS_MID 0x3a 8 LoadedBU_DISPADDR_COMP2_VBS_LSB 0x3b 8 BU_ADDR_COMP0_HBS_MSB 0x3d 2 Must beBU_ADDR_COMP0_HBS_MID 0x3e 8 Loaded BU_ADDR_COMP0_HBS_LSB 0x3f 8BU_ADDR_COMP1_HBS_MSB 0x41 2 Must be BU_ADDR_COMP1_HBS_MID 0x42 8 LoadedBU_ADDR_COMP1_HBS_LSB 0x43 8 BU_ADDR_COMP2_HBS_MSB 0x45 2 Must beBU_ADDR_COMP2_HBS_MID 0x46 8 Loaded BU_ADDR_COMP2_HBS_LSB 0x47 8BU_DISPADDR_COMP0_HBS_MSB 0x49 2 Must be BU_DISPADDR_COMP0_HBS_MID 0x4a8 Loaded BU_DISPADDR_COMP0_HBS_LSB 0x4b 8 BU_DISPADDR_COMP1_HBS_MSB 0x4d2 Must be BU_DISPADDR_COMP1_HBS_MID 0x4e 8 LoadedBU_DISPADDR_COMP1_HBS_LSB 0x4f 8 BU_DISPADDR_COMP2_HBS_MSB 0x51 2 Mustbe BU_DISPADDR_COMP2_HBS_MID 0x52 8 Loaded BU_DISPADDR_COMP2_HBS_LSB0x53 8 BU_DISPADDR_CNT_LEFT0_MSB 0x55 2 Test onlyBU_DISPADDR_CNT_LEFT0_MID 0x56 8 BU_DISPADDR_CNT_LEFT0_LSB 0x57 8BU_DISPADDR_CNT_LEFT1_MSB 0x59 2 Test only BU_DISPADDR_CNT_LEFT1_MID0x5a 8 BU_DISPADDR_CNT_LEFT1_LSB 0x5b 8 BU_DISPADDR_CNT_LEFT2_MSB 0x5d 2Test only BU_DISPADDR_CNT_LEFT2_MID 0x5e 8 BU_DISPADDR_CNT_LEFT2_LSB0x5f 8 BU_DISPADDR_PAGE_ADDR0_MSB 0x61 2 Test onlyBU_DISPADDR_PAGE_ADDR0_MID 0x62 8 BU_DISPADDR_PAGE_ADDR0_LSB 0x63 8BU_DISPADDR_PAGE_ADDR1_MSB 0x65 2 Test only BU_DISPADDR_PAGE_ADDR1_MID0x66 8 BU_DISPADDR_PAGE_ADDR1_LSB 0x67 8 BU_DISPADDR_PAGE_ADDR2_MSB 0x692 Test only BU_DISPADDR_PAGE_ADDR2_MID 0x6a 8 BU_DISPADDR_PAGE_ADDR2_LSB0x6b 8 BU_DISPADDR_BLOCK_ADDR0_MSB 0x6d 2 Test onlyBU_DISPADDR_BLOCK_ADDR0_MID 0x6e 8 BU_DISPADDR_BLOCK_ADDR0_LSB 0x6f 8BU_DISPADDR_BLOCK_ADDR1_MSB 0x71 2 Test only BU_DISPADDR_BLOCK_ADDR1_MID0x72 8 BU_DISPADDR_BLOCK_ADDR1_LSB 0x73 8 BU_DISPADDR_BLOCK_ADDR2_MSB0x75 2 Test only BU_DISPADDR_BLOCK_ADDR2_MID 0x76 8BU_DISPADDR_BLOCK_ADDR2_LSB 0x77 8 BU_DISPADDR_BLOCKS_LEFT0_MSB 0x79 2Test only BU_DISPADDR_BLOCKS_LEFT0_MID 0x7a 8BU_DISPADDR_BLOCKS_LEFT0_LSB 0x7b 8 BU_DISPADDR_BLOCKS_LEFT1_MSB 0x7d 2Test only BU_DISPADDR_BLOCKS_LEFT1_MID 0x7e 8BU_DISPADDR_BLOCKS_LEFT1_LSB 0x7f 8 BU_DISPADDR_BLOCKS_LEFT2_MSB 0x81 2Test only BU_DISPADDR_BLOCKS_LEFT2_MID 0x82 8BU_DISPADDR_BLOCKS_LEFT2_LSB 0x83 8 BU_WADDR_BUFFER0_BASE_MSB 0x85 2Must be BU_WADDR_BUFFER0_BASE_MID 0x86 8 LoadedBU_WADDR_BUFFER0_BASE_LSB 0x87 8 BU_WADDR_BUFFER1_BASE_MSB 0x89 2 Mustbe BU_WADDR_BUFFER1_BASE_MID 0x8a 8 Loaded BU_WADDR_BUFFER1_BASE_LSB0x8b 8 BU_WADDR_BUFFER2_BASE_MSB 0x8d 2 Must beBU_WADDR_BUFFER2_BASE_MID 0x8e 8 Loaded BU_WADDR_BUFFER2_BASE_LSB 0x8f 8BU_WADDR_COMP0_HMBADDR_MSB 0x91 2 Test only BU_WADDR_COMP0_HMBADDR_MID0x92 8 BU_WADDR_COMP0_HMBADDR_LSB 0x93 8 BU_WADDR_COMP1_HMBADDR_MSB 0x952 Test only BU_WADDR_COMP1_HMBADDR_MID 0x96 8 BU_WADDR_COMP1_HMBADDR_LSB0x97 8 BU_WADDR_COMP2_HMBADDR_MSB 0x99 2 Test onlyBU_WADDR_COMP2_HMBADDR_MID 0x9a 8 BU_WADDR_COMP2_HMBADDR_LSB 0x9b 8BU_WADDR_COMP0_VMBADDR_MSB 0x9d 2 Test only BU_WADDR_COMP0_VMBADDR_MID0x9e 8 BU_WADDR_COMP0_VMBADDR_LSB 0x9f 8 BU_WADDR_COMP1_VMBADDR_MSB 0xa12 Test only BU_WADDR_COMP1_VMBADDR_MID 0xa2 8 BU_WADDR_COMP1_VMBADDR_LSB0xa3 8 BU_WADDR_COMP2_VMBADDR_MSB 0xa5 2 Test onlyBU_WADDR_COMP2_VMBADDR_MID 0xa6 8 BU_WADDR_COMP2_VMBADDR_LSB 0xa7 8BU_WADDR_VBADDR_MSB 0xa9 2 Test only BU_WADDR_VBADDR_MID 0xaa 8BU_WADDR_VBADDR_LSB 0xab 8 BU_WADDR_COMP0_HALF_WIDTH_IN_BLOCKS_MSB 0xad2 Must be BU_WADDR_COMP0_HALF_WIDTH_IN_BLOCKS_MID 0xae 8 LoadedBU_WADDR_COMP0_HALF_WIDTH_IN_BLOCKS_LSB 0xaf 8BU_WADDR_COMP1_HALF_WIDTH_IN_BLOCKS_MSB 0xb1 2 Must beBU_WADDR_COMP1_HALF_WIDTH_IN_BLOCKS_MID 0xb2 8 LoadedBU_WADDR_COMP1_HALF_WIDTH_IN_BLOCKS_LSB 0xb3 8BU_WADDR_COMP2_HALF_WIDTH_IN_BLOCKS_MSB 0xb5 2 Must beBU_WADDR_COMP2_HALF_WIDTH_IN_BLOCKS_MID 0xb6 8 LoadedBU_WADDR_COMP2_HALF_WIDTH_IN_BLOCKS_LSB 0xb7 8 BU_WADDR_HB_MSB 0xb9 2Test only BU_WADDR_HB_MID 0xba 8 BU_WADDR_HB_LSB 0xbb 8BU_WADDR_COMP0_OFFSET_MSB 0xbd 2 Must be BU_WADDR_COMP0_OFFSET_MID 0xbe8 Loaded BU_WADDR_COMP0_OFFSET_LSB 0xbf 8 BU_WADDR_COMP1_OFFSET_MSB 0xc12 Must be BU_WADDR_COMP1_OFFSET_MID 0xc2 8 LoadedBU_WADDR_COMP1_OFFSET_LSB 0xc3 8 BU_WADDR_COMP2_OFFSET_MSB 0xc5 2 Mustbe BU_WADDR_COMP2_OFFSET_MID 0xc6 8 Loaded BU_WADDR_COMP2_OFFSET_LSB0xc7 8 BU_WADDR_SCRATCH_MSB 0xc9 2 Test only BU_WADDR_SCRATCH_MID 0xca 8BU_WADDR_SCRATCH_LSB 0xcb 8 BU_WADDR_MBS_WIDE_MSB 0xcd 2 Must beBU_WADDR_MBS_WIDE_MID 0xce 8 Loaded BU_WADDR_MBS_WIDE_LSB 0xcf 8BU_WADDR_MBS_HIGH_MSB 0xd1 2 Must be BU_WADDR_MBS_HIGH_MID 0xd2 8 LoadedBU_WADDR_MBS_HIGH_LSB 0xd3 8 BU_WADDR_COMP0_LAST_MB_IN_ROW_MSB 0xd5 2Must be BU_WADDR_COMP0_LAST_MB_IN_ROW_MID 0xd6 8 LoadedBU_WADDR_COMP0_LAST_MB_IN_ROW_LSB 0xd7 8BU_WADDR_COMP1_LAST_MB_IN_ROW_MSB 0xd9 2 Must beBU_WADDR_COMP1_LAST_MB_IN_ROW_MID 0xda 8 LoadedBU_WADDR_COMP1_LAST_MB_IN_ROW_LSB 0xdb 8BU_WADDR_COMP2_LAST_MB_IN_ROW_MSB 0xdd 2 Must beBU_WADDR_COMP2_LAST_MB_IN_ROW_MID 0xde 8 LoadedBU_WADDR_COMP2_LAST_MB_IN_ROW_LSB 0xdf 8BU_WADDR_COMP0_LAST_MB_IN_HALF_ROW_MSB 0xe1 2 Must beBU_WADDR_COMP0_LAST_MB_IN_HALF_ROW_MID 0xe2 8 LoadedBU_WADDR_COMP0_LAST_MB_IN_HALF_ROW_LSB 0xe3 8BU_WADDR_COMP1_LAST_MB_IN_HALF_ROW_MSB 0xe5 2 Must beBU_WADDR_COMP1_LAST_MB_IN_HALF_ROW_MID 0xe6 8 LoadedBU_WADDR_COMP1_LAST_MB_IN_HALF_ROW_LSB 0xe7 8BU_WADDR_COMP2_LAST_MB_IN_HALF_ROW_MSB 0xe9 2 Must beBU_WADDR_COMP2_LAST_MB_IN_HALF_ROW_MID 0xea 8 LoadedBU_WADDR_COMP2_LAST_MB_IN_HALF_ROW_LSB 0xeb 8BU_WADDR_COMP0_LAST_ROW_IN_MB_MSB 0xed 2 Must beBU_WADDR_COMP0_LAST_ROW_IN_MB_MID 0xee 8 LoadedBU_WADDR_COMP0_LAST_ROW_IN_MB_LSB 0xef 8BU_WADDR_COMP1_LAST_ROW_IN_MB_MSB 0xf1 2 Must beBU_WADDR_COMP1_LAST_ROW_IN_MB_MID 0xf2 8 LoadedBU_WADDR_COMP1_LAST_ROW_IN_MB_LSB 0xf3 8BU_WADDR_COMP2_LAST_ROW_IN_MB_MSB 0xf5 2 Must beBU_WADDR_COMP2_LAST_ROW_IN_MB_MID 0xf6 8 LoadedBU_WADDR_COMP2_LAST_ROW_IN_MB_LSB 0xf7 8BU_WADDR_COMP0_BLOCKS_PER_MB_ROW_MSB 0xf9 2 Must beBU_WADDR_COMP0_BLOCKS_PER_MB_ROW_MID 0xfa 8 LoadedBU_WADDR_COMP0_BLOCKS_PER_MB_ROW_LSB 0xfb 8BU_WADDR_COMP1_BLOCKS_PER_MB_ROW_MSB 0xfd 2 Must beBU_WADDR_COMP1_BLOCKS_PER_MB_ROW_MID 0xfe 8 LoadedBU_WADDR_COMP1_BLOCKS_PER_MB_ROW_LSB 0xff 8BU_WADDR_COMP2_BLOCKS_PER_MB_ROW_MSB 0x101 2 Must beBU_WADDR_COMP2_BLOCKS_PER_MB_ROW_MID 0x102 8 LoadedBU_WADDR_COMP2_BLOCKS_PER_MB_ROW_LSB 0x103 8BU_WADDR_COMP0_LAST_MB_ROW_MSB 0x105 2 Must beBU_WADDR_COMP0_LAST_MB_ROW_MID 0x106 8 LoadedBU_WADDR_COMP0_LAST_MB_ROW_LSB 0x107 8 BU_WADDR_COMP1_LAST_MB_ROW_MSB0x109 2 Must be BU_WADDR_COMP1_LAST_MB_ROW_MID 0x10a 8 LoadedBU_WADDR_COMP1_LAST_MB_ROW_LSB 0x10b 8 BU_WADDR_COMP2_LAST_MB_ROW_MSB0x10d 2 Must be BU_WADDR_COMP2_LAST_MB_ROW_MID 0x10e 8 LoadedBU_WADDR_COMP2_LAST_MB_ROW_LSB 0x10f 8 BU_WADDR_COMP0_HBS_MSB 0x111 2Must be BU_WADDR_COMP0_HBS_MID 0x112 8 Loaded BU_WADDR_COMP0_HBS_LSB0x113 8 BU_WADDR_COMP1_HBS_MSB 0x115 2 Must be BU_WADDR_COMP1_HBS_MID0x116 8 Loaded BU_WADDR_COMP1_HBS_LSB 0x117 8 BU_WADDR_COMP2_HBS_MSB0x119 2 Must be BU_WADDR_COMP2_HBS_MID 0x11a 8 LoadedBU_WADDR_COMP2_HBS_LSB 0x11b 8 BU_WADDR_COMP0_MAXHB 0x11f 2 Must beBU_WADDR_COMP1_MAXHB 0x123 2 Loaded BU_WADDR_COMP2_MAXHB 0x127 2BU_WADDR_COMP0_MAXVB 0x12b 2 Must be BU_WADDR_COMP1_MAXVB 0x12f 2 LoadedBU_WADDR_COMP2_MAXVB 0x133 2

[3497] C.12.3 Horizontal Upsampler and Color Space Converter KeyholeTABLE C.11.3 H-Upsamplers and Cspace Keyhole Address Map KeyholeRegister Keyhole Name Address Bits Comment BU_UH0_A00_1 0x0 5 R/W -Coeff 0.0 BU_UH0_A00_0 0x1 8 BU_UH0_A01_1 0x2 5 R/W - Coeff 0.1BU_UH0_A01_0 0x3 8 BU_UH0_A02_1 0x4 5 R/W - Coeff 0.2 BU_UH0_A02_0 0x5 8BU_UH0_A03_1 0x6 5 R/W - Coeff 0.0 BU_UH0_A03_0 0x7 8 BU_UH0_A10_1 0x8 5R/W - Coeff 1.0 BU_UH0_A10_0 0x9 8 BU_UH0_A11_1 0xa 5 R/W - Coeff 1.1BU_UH0_A11_0 0xb 8 BU_UH0_A12_1 0xc 5 R/W - Coeff 1.2 BU_UH0_A12_0 0xd 8BU_UH0_A13_1 0xe 5 R/W - Coeff 1.3 BU_UH0_A13_0 0xf 8 BU_UH0_A20_1 0x105 R/W - Coeff 2.0 BU_UH0_A20_0 0x11 8 BU_UH0_A21_1 0x12 5 R/W - Coeff2.1 BU_UH0_A21_0 0x13 8 BU_UH0_A22_1 0x14 5 R/W - Coeff 2.2 BU_UH0_A22_00x15 8 BU_UH0_A23_1 0x16 5 R/W - Coeff 2.3 BU_UH0_A23_0 0x17 8BU_UH0_MODE 0x18 2 R/W BU_UH1_A00_1 0x20 5 R/W - Coeff 0.0 BU_UH1_A00_00x21 8 BU_UH1_A01_1 0x22 5 R/W - Coeff 0.1 BU_UH1_A01_0 0x23 8BU_UH1_A02_1 0x24 5 R/W - Coeff 0.2 BU_UH1_A02_0 0x25 8 BU_UH1_A03_10x26 5 R/W - Coeff 0.0 BU_UH1_A03_0 0x27 8 BU_UH1_A10_1 0x28 5 R/W -Coeff 1.0 BU_UH1_A10_0 0x29 8 BU_UH1_A11_1 0x2a 5 R/W - Coeff 1.1BU_UH1_A11_0 0x2b 8 BU_UH1_A12_1 0x2c 5 R/W - Coeff 1.2 BU_UH1_A12_00x2d 8 BU_UH1_A13_1 0x2e 5 R/W - Coeff 1.3 BU_UH1_A13_0 0x2f 8BU_UH1_A20_1 0x30 5 R/W - Coeff 2.0 BU_UH1_A20_0 0x31 8 BU_UH1_A21_10x32 5 R/W - Coeff 2.1 BU_UH1_A21_0 0x33 8 BU_UH1_A22_1 0x34 5 R/W -Coeff 2.2 BU_UH1_A22_0 0x35 8 BU_UH1_A23_1 0x36 5 R/W - Coeff 2.3BU_UH1_A23_0 0x37 8 BU_UH1_MODE 0x38 2 R/W BU_UH2_A00_1 0x40 5 R/W -Coeff 0.0 BU_UH2_A00_0 0x41 8 BU_UH2_A01_1 0x42 5 R/W - Coeff 0.1BU_UH2_A01_0 0x43 8 BU_UH2_A02_1 0x44 5 R/W - Coeff 0.2 BU_UH2_A02_00x45 8 BU_UH2_A03_1 0x46 5 R/W - Coeff 0.0 BU_UH2_A03_0 0x47 8BU_UH2_A10_1 0x48 5 R/W - Coeff 1.0 BU_UH2_A10_0 0x49 8 BU_UH2_A11_10x4a 5 R/W - Coeff 1.1 BU_UH2_A11_0 0x4b 8 BU_UH2_A12_1 0x4c 5 R/W -Coeff 1.2 BU_UH2_A12_0 0x4d 8 BU_UH2_A13_1 0x4e 5 R/W - Coeff 1.3BU_UH2_A13_0 0x4f 8 BU_UH2_A20_1 0x50 5 R/W - Coeff 2.0 BU_UH2_A20_00x51 8 BU_UH2_A21_1 0x52 5 R/W - Coeff 2.1 BU_UH2_A21_0 0x53 8BU_UH2_A22_1 0x54 5 R/W - Coeff 2.2 BU_UH2_A22_0 0x55 8 BU_UH2_A23_10x56 5 R/W - Coeff 2.3 BU_UH2_A23_0 0x57 8 BU_UH2_MODE 0x58 2 R/WBU_CS_A00_1 0x60 5 R/W BU_CS_A00_0 0x61 8 BU_CS_A10_1 0x62 5 R/WBU_CS_A10_0 0x63 8 BU_CS_A20_1 0x64 5 R/W BU_CS_A20_0 0x65 8 BU_CS_B0_10x66 6 R/W BU_CS_B0_0 0x67 8 BU_CS_A01_1 0x68 5 R/W BU_CS_A01_0 0x69 8BU_CS_A11_1 0x6a 5 R/W BU_CS_A11_0 0x6b 8 BU_CS_A21_1 0x6c 5 R/WBU_CS_A21_0 0x6d 8 BU_CS_B1_1 0x6e 6 R/W BU_CS_B1_0 0x6f 8 BU_CS_A02_10x70 5 R/W BU_CS_A02_0 0x71 8 BU_CS_A12_1 0x72 5 R/W BU_CS_A12_0 0x73 8BU_CS_A22_1 0x74 5 R/W BU_CS_A22_0 0x75 8 BU_CS_B2_1 0x76 5 R/WBU_CS_B2_0 0x77 8

[3498] SECTION C.13 Picture Size Parameters

[3499] C.13.1 Introduction

[3500] The following stylized code fragments illustrate the processingnecessary to respond to picture size interrupts from the write addressgenerator. Note that the picture size parameters can be changed“on-the-fly” by sending combinations of HORIZONTAL_MBS, VERTICAL_MBS,and DEFINE_SAMPLING (for each component) tokens, resulting in writeaddress generator interrupts. These tokens may arrive in any order and,in general, any one should necessitate the re-calculation of all of thepicture size parameters. At setup time, however, it would be moreefficient to detect the arrival of all of the events before performingany calculations.

[3501] It is possible to write specific values into the picture sizeparameter registers at setup and, therefore, to not rely on interruptprocessing in response to tokens. For this reason, the appropriateregister values for SIF pictures are also given.

[3502] C.13.2 Interrupt Processing for Picture Size Parameters

[3503] There are five picture size events, and the primary response ofeach is given below: if (hmbs_event; load(mbs_wide); else if(vmbs_event) load(mbs_high); else if (def_samp0_event) { load(maxhb[0]); load (maxvb[0!]); } else if (def_samp1_event) { load(maxhb[1]); load (maxhb[2]); } else if (def_samp2_event) { load(maxvb[2!]; load (maxhb[2]); }

[3504] In addition, the following calculations are necessary to retainconsistent picture size paramneters: if (hmbs_event||vmbs_event||def_samp0_event||def_samp1_event||def_samp2_event; { for (i=0;i<max_component; i++) { hbs[i] = addr_hbs[i] = (maxhb[i]+1) * mbs_wide;half_width_in_blocks[i] = ((maxhb[i]+1) * mbs_wide)/2; last_mb_in_row[i]= hbs[i] − (maxhb[i]+1); last_mb_in_half_row[i] =half_width_in_blocks[i]+ (maxhb[i]+1); last_row_in_mb[i] = hbs[i] *maxvb[i]; blocks_per_mb_row[i] = last_row_in_mb[i]+ hbs[i];last_mb_row[i] = blocks_per_mb_row[i] * (mbs_high-1); } }

[3505] Although it is not strictly necessary to modify the dispaddrregister values (such as the display window size) in response to picturesize interrupts, this may be desirable depending on the applicationrequirements.

[3506] C.13.3 Register Values for SIF Pictures

[3507] The values contained in all the picture size registers after theabove interrupt processing for an SIF, 4:2:0 stream will be as follows:

[3508] C.13.3.1 Primary Values

[3509] BU_WADDR_WIDE=0×16

[3510] BU_WADOR_Mes_HIGH=0×12

[3511] BU_WADDR_COMP0_MAXHB=0×01

[3512] BU_WADDR_COMP1_MAXHB=0×00

[3513] BU_WADDR_COMP2_MAXHB=0×00

[3514] BU_WADDR_COMP0_MAXVB=0×01

[3515] BU_WADDR_COMP1_MAXVB=0×00

[3516] BU_WADDR_COMP2_MAVVB=0×00

[3517] C.13.3.2 Secondary Values After Calculation

[3518] BU_WADDR_COMP0_HBS=0×2C

[3519] BU_WADDR_COMP1_HBS=0×16

[3520] BU_WADDR_COMP2_HBS=0×16

[3521] BU_ADDR_COMP0_HBS=0×2C

[3522] BU_ADDR_COMP1_HBS=0×16

[3523] BU_ADDR_COMP2_HBS=0×16

[3524] BU_WADDR_COMP0_HALF_WIDTH_IN_BLOCKS=0×16

[3525] BU_WADDR_COMP1_HALF_WIDTH_IN_BLOCKS=0×0B

[3526] BU_WADDR_COMP2_HALF_WIDTH_IN_BLOCKS=0×0B

[3527] BU_WADDR_COMP0_LAST_MB_IN_ROW=0×2A

[3528] BU_WADDR_COMP1_LAST_MB_IN_ROW=0×15

[3529] BU_WADDR_COMP2_LAST_MB_IN_ROW=0×15

[3530] BU_WADDR_COMP0_LAST_MB_IN_HALF_ROW=0×14

[3531] BU_WADDR_COMP1_LAST_MB_IN_HALF_ROW=0×0A

[3532] BU_WADDR_COMP2_LAST_MB_IN_HALF_ROW=0×0A

[3533] BU_WADDR_COMP0_LAST_ROW_IN_MB=0×2C

[3534] BU_WADDR_COMP1_LAST_ROW_IN_MB=0×0

[3535] BU_WADDR_COMP2_LAST_ROW_IN_MB=0×0

[3536] BU_WADDR_COMP0_BLOCKS_PER_MB_ROW=0×58

[3537] BU_WADDR_COMP1_BLOCKS_PER_MB_ROW=0×16

[3538] BU_WADDR_COMP2_BLOCKS_PER_MB_ROW=0×16

[3539] BU_WADDR_COMP0_LAST_MB_ROW=0×5D8

[3540] BU_WADDR_COMP1_LAST_MB_ROW=0×176

[3541] BU_WADDR_COMP2_LAST_MB_ROW=0×176

[3542] Note that if these values are to be written explicitly at setup,account must be taken of the multi-byte nature of most of the locations.

[3543] Note that additional Figures, which are self explanatory to thoseof ordinary skill in the art, are included with this application forproviding further insight into the detailed structure and operation ofthe environment in which the present invention is intended to function.

[3544] The aforedescribed pipeline system of the present inventionsatisfies a long existing need for an improved system having an input,an output and a plurality of processing stages between the input and theoutput, the plurality of processing stages being interconnected by atwo-wire interface for conveyance of tokens along the pipeline, andcontrol and/or DATA tokens in the form of universal adaptation units forinterfacing with all of the processing stages in the pipeline andinteracting with selected stages in the pipeline for control data and/orcombined control-data functions among the processing stages, so that theprocessing stages in the pipeline are afforded enhanced flexibility inconfiguration and processing. In accordance with the invention, theprocessing stages may be configurable in response to recognition of atleast one token. One of the processing stages may be a Start CodeDetector which receives the input and generates and/or converts thetokens.

[3545] The present invention also relates to an improved pipeline systemhaving a spatial decoder system for video data including a Huffmandecoder, an index to data and an arithmetic logic unit, and a microcodeROM having separate stored programs for each of a plurality of differentpicture compression/decompression standards, such programs beingselectable by a token, whereby processing for a plurality of differentpicture standards is facilitated. The present invention may also includetokens in the form of a PICTURE_START code token for indicating that thestart of a picture will follow in the subsequent DATA token, aPICTURE_END token for indicating the end of an individual picture, aFLUSH token for clearing buffers and resetting the system, and aCODING_STANDARD token for conditioning the system for processing in aselected one of a plurality of picture compression/decompressionstandards. The present invention also relates to an improved pipelinesystem for decoding video data and having a Huffman decoder, an index todata (ITOD) stage, an arithmetic logic unit (ALU), and a data bufferingmeans immediately following the system, whereby time spread for videopictures of varying data size can be controlled. Also in accordance withthe invention, a processing stage receives the input data stream, thestage including means for recognizing specified bit stream patterns,whereby the processing stage facilitates random access and errorrecovery. The invention may also include a means for performing astop-after-picture operation for achieving a clear end to picture datadecoding, for indicating the end of a picture, and for clearing thepipeline.

[3546] The improved pipeline system may also include a fixed size, fixedwidth buffer, and means for padding the buffer to pass an arbitrarynumber of bits through the buffer. The present invention also relates toa data stream including run length code, and an inverse modeller meansactive upon the data stream from a token for expanding out the run levelcode to a run of zero data followed by a level, whereby each token isexpressed with a specified number of values. The invention also includesan inverse modeller stage, an inverse discrete cosine transform stage,and a processing stage, positioned between the inverse modeller stageand the inverse discrete cosine transform stage, responsive to a tokentable for processing data.

[3547] In addition, the present invention relates to an improvedpipeline system having a Huffman decoder for decoding data words encodedaccording to the Huffman coding provisions of either H.261, JPEG or MPEGstandards, the data words including an identifier that identifies theHuf fman code standard under which the data words were coded, means forreceiving the Huffman coded data words, means for reading the identifierto determine which standard governed the Huffman coding of the receiveddata words, if necessary, in response to reading the identifier thatidentifies the Huffman coded data words as H.261 or MPEG Huffman coded,means operably connected to the Huffman coded data words receiving meansfor generating an index number associated with each JPEG Huffman codeddata word received from the Huffman coded data words receiving means,means for operating a lookup table containing a Huffman code tablehaving the format used under the JPEG standard to transmit JPEG Huffmantable information, including an input for receiving an index number fromthe index number generating means, and including an output that is adecoded data word corresponding to the index number.

[3548] The improved system includes a multi-standard video decompressionapparatus having a plurality of stages interconnected by a two-wireinterface arranged as a pipeline processing machine. Control tokens andDATA Tokens pass over the single two-wire interface for carrying bothcontrol and data in token format. A token decode circuit is positionedin certain of the stages for recognizing certain of the tokens ascontrol tokens pertinent to that stage and for passing unrecognizedcontrol tokens along the pipeline. Reconfiguration processing circuitsare positioned in selected stages and are responsive to a recognizedcontrol token for reconfiguring such stage to handle an identified DATAToken. A wide variety of unique supporting subsystem circuitry andprocessing techniques are disclosed for implementing the system.

[3549] It will be apparent from the foregoing that, while particularforms of the invention have been illustrated and described, variousmodification can be made without departing from the spirit and scope ofthe invention. Accordingly, it is not intended that the invention belimited, except as by the appended claims.

In the claims:
 1. An apparatus comprising: a port coupled to receivecontrol tokens from a decoder circuit that decodes video data havingmultiple different formats and stores the decoded video data in amemory; and a formatter coupled to retrieve the decoded video data fromthe memory in response to the received control tokens and sends theretrieved decoded video data to a display system.
 2. The apparatus ofclaim 1, wherein the formatter comprises an address generator forgenerating addresses from the control tokens.
 3. The apparatus of claim2, wherein formatter further comprises: a memory interface forcontrolling the transfer of the decoded video data from the memory usingthe addresses generated by the address generator.
 4. The apparatus ofclaim 1, wherein the formatter comprises buffers for storing the decodedvideo data, one of the buffers being a display buffer and another of thebuffers being an arrival buffer.
 5. The apparatus of claim 1, furthercomprising: a buffer manager, responsive to arrival rates, display ratesand frame rates, of the decoded video data, for allocating the buffersto the address generator.
 6. A method of formatting decoded video datacomprising: receiving control tokens; and in response to receivingcontrol tokens, retrieving decoded video data from a memory and sendingthe retrieved decoded video data to a display system.
 7. The method ofclaim 6, wherein the retrieving step comprises: generating addressesfrom the control tokens.
 8. The method of claim 6, wherein theretrieving step further comprises: providing an interface to memory. 9.The method of claim 8, wherein the providing an interface stepcomprises: providing a display buffer and an arrival buffer.
 10. Themethod of claim 9, further comprising: allocating buffers in the displaybuffer and arrival buffer to the address generator according to at leastone of the arrival rates, display rates, and frame rates associated withthe decoded video data stored in the memory.